Big question for Bears — why was Josh Sitton available?

“What do the Packers know that we don’t?”

That’s the question Bears general manager Ryan Pace should have been asking himself when he contemplated signing former Packers Pro Bowl guard Josh Sitton this weekend. Sitton seems like a gift from the football gods for the Bears. He just turned 30 in June. He was a second-team All-Pro selection in 2015. He can play guard or center. And he has the nasty football mentality everybody loves. This is a guy who played in 88-of-90 games and made the Pro Bowl three times after signing the big contract extension in 2011 (five years, $33.75 million) — when he had never made the Pro Bowl before. He’s just what the Bears need.

Then again, the Packers had to know that when they decided to cut Sitton after being unable to trade him last week, so the question remains, what does Ted Thompson know that Ryan Pace does not? Sitton was in the last year of his contract and likely to ask for a raise in the new deal. But why wouldn’t the Packers let him play out his old deal and walk? That’s a red flag right there.

The Packers — like the gold-standard Patriots — are a prudent organization with a strict adherance to cost-efficiency. Once your cap hit outstrips your production, you’re vulnerable. Two years ago, the Patriots suddenly traded guard Logan Mankins — a team captain, a Pro Bowl player the previous season and the heart-and-soul of their offensive line — to the Buccaneers at cut-down time. They moved their right guard to left guard, their center to right guard and inserted rookie Bryan Stork at center — and won the Super Bowl. Mankins played one inglorious season with the Buccaneers and retired.

That’s the kind of intuition successful NFL organizations have — though getting the quarterback right sure helps make any move turn to gold.

But therein lies the challenge for Ryan Pace, who at 39 is still trying to get his footing in his second season as general manager. Why was Josh Sitton available? Was Sitton just a cost-efficiency move by the Packers? How much does he have left?

Evaluations of offensive linemen vary wildly in the NFL. Many of us thought Matt Slauson was the Bears’ best lineman last year. The Bears saw him as a back-up at best. The Chargers see him as a starter. The Packers thought Sitton wasn’t worth $6.55 million. The Bears think he’s worth more than that — they signed him to a three-year contract worth a reported $21.75 million, with $10 million guaranteed. Ted Thompson makes his share of mistakes. We’ll if Ryan Pace is right that this is one of them.

2. Along those lines, when Pernell McPhee was a free agent in 2015, a big question was why the Ravens would let a 26-year-old pass rusher get to free agency? The speculation was that McPhee was injury prone and wouldn’t last as a full-time player.

At this point it looks like those concerns were well-founded. McPhee was productive early last season but faded because of a knee issue. Now he’s on the physically unable to perform (PUP) list, which will force him to miss the first six games of the regular season. It’s too early to call McPhee a whiff by Pace, but the early returns are not good for the Bears. Unless McPhee recovers and stays healthy and productive, the questions are inevitable: Should the Bears have shut down McPhee at the first sign of trouble last season instead of letting him play through it? Should McPhee have had the surgery before the end of the season? And, should the Bears have even signed McPhee in the first place?

3. For a team that has put such an emphasis on sports medicine, sports nutrition and rehabilitation, the Bears haven’t had much luck with injuries.

McPhee had arthroscopic surgery after the 2015 season — generally not a long-term recovery — but won’t return until October at the earliest. In June, Marquess Wilson broke the same foot that was surgically repaired in December. And Kevin White missed all of last season after being day-to-day with a stress fracture at the start of training camp in 2015.

The Bears have had some success stories under Pace. Willie Young and Lamarr Houston recovered from major surgery to post productive seasons last year. Tracy Porter missed most of camp but ended up being the Bears best cornerback and earned a long-term contract. But the long recoveries have been more glaring — in part because the Bears are so secretive about injury information. At this point, they’d be better off being transparent and just giving us a worst-case-scenario — “Pernell McPhee might not be ready for the opener” — and then it’s not such a disappointment when he starts the year on PUP, or better yet, a pleasant surprise if he returns earlier.

Meanwhile, in Houston, three-time NFL defensive player of the year J.J. Watt is expected to play against the Bears in Week 1 — after undergoing surgery to repair a herniated disk on July 19.

4. It wasn’t going to happen overnight, so it’s no surprise that the Bears have a lot of catching up to do in building a roster of home-grown talent. Just 27 players on the 53-man roster were drafted or signed out of college by the Bears, including 20 draft picks.

Here’s how the Bears compare to the rest of NFC North:

First-round picks (originally drafted by any team): Vikings 13, Packers 9, Lions 7, Bears 5.

Home-grown players: Packer 49, Vikings 37, Lions 32, Bears 27.

Their own draft picks: Packers 35, Vikings 31, Lions 28, Bears 20.

Undrafted players: Bears 17, Packers 15, Vikings 15, Lions 14.

5. The Bears have eight rookies on their 53-man roster, though interestingly, none of their undrafted free agents made it. The Packers have 13 rookies on their 53-man roster, including six undrafted players. Among the Packers’ undrafted free agents is Makinton Dorleant, who played cornerback at Northern Iowa with Bears rookie Deiondre Hall last season and was kept on the 53-man roster despite twice injuring his hamstring.

6. The Bears have 15 players acquired by former general manager Phil Emery on their 53-man roster, including wide receiver Alshon Jeffery, right guard Kyle Long, outside linebackers Willie Young and Lamarr Houston, left tackle Charles Leno and punter Pat O’Donnell. Last year they had 28 Emery-acquired players on the 53-man roster.

After Robbie Gould was cut, Jay Cutler is the only Jerry Angelo-acquired player on the Bears’ roster.

7. The starting offensive line in Week 1 last season (from left to right) was Jermon Bushrod, Matt Slauson, Will Montgomery, Vladimir Ducasse and Kyle Long. This year it figures to be Charles Leno, Josh Sitton, Cody Whitehair, Long and Bobby Massie — and that’s only if Long is healthy enough to play. Either way, one of the Bears’ top priorities has to be establishing continuity on the offensive line. Only Long started every game in the same position last season.

For what it’s worth, six former Bears offensive linemen are still in the NFL: Slauson (Chargers), Jermon Bushrod (Dolphins), Jordan Mills (Bills), Patrick Omameh (Jaguars), Ryan Groy (Bills) and (drumroll, please) J’Marcus Webb (Seahawks.)

8. Ex-Bears of the Preseason —This offense comprised of former Bears still in the NFL doesn’t look bad on paper:

QB Josh McCown; RB Matt Forte; LT Jermon Bushrod; LG Ryan Groy; C Matt Slauson; RG Patrick Omameh; RT Jordan Mills; TE Martellus Bennett/Greg Olsen; WR Brandon Marshall/Devin Hester.

9. It’s all about player development for the Bears in 2016. If these lists of the top players on offense and defense are the same after Week 17, the Bears likely will not have made a lot of progress:

Offense: 1. Kyle Long; 2. Alshon Jeffery; 3. Jay Cutler; 4. Zach Miller; 5. Eddie Royal.

Defense: 1. Danny Trevathan; 2. Akiem Hicks; 3. Tracy Porter; 4. Willie Young; 5. Jerrell Freeman.

10. This Bears team looks like it will fall into the 7-9 to 9-7 range, with a greater chance to finish 10-6 than 4-12. The upside: Fox/Fangio teams develop in their second year; Downside: Bears just can’t get healthy or stay healthy. The schedule:

at Texans (L); Eagles (W); at Cowboys (L); Lions (W); at Colts (L); Jaguars (W); at Packers (L); Vikings (L); at Buccaneers (W); at Giants (L); Titans (W); 49ers (W); at Lions (W); Packers (L); Redskins (W); at Vikings (L). Record: 8-8.

Just don’t bet on it. That could be a year of wild fluctuations for the Bears.