Adams definitely talked to Reinhart about staying and he was told that Reinhart wanted to move on. The error of not extending Reinhart was on Botterill, not Adams. And even if he had locked up Reinhart (like Eichel), that was no guarantee we would have kept him.
Mitts is a completely different situation than that and I have no problem with the way Adams has handled it. You can't offer everyone a long term deal, you just can't. He identified the young core pieces and locked them up, which I still believe was/is the right thing to do. Now, you're either trading Mitts, or looking to sign him shorter term, and as such, you're negotiating. Why would you have made an offer before this season when he's an RFA and you aren't in danger of losing him, especially because I'm sure Adams knows Mitts wants to stay.
Offering Mitts a long term deal would just further limit our flexibility, making it harder to build out our roster, and harder to trade him. There's just no reason to do that at this point and people piling on Adams for it are just upset about the season and trying to pin everything on him.
If we want to be critical of Adams, it's not like there aren't other clear issues. Not doing anything to significantly improve the defense for multiple years is the #1 issue I have with the job he's done. I continue to believe it's the biggest thing holding this team back and until he makes a significant move there, we'll continue to struggle to make the playoffs.