Others have answered the question well. I will add that Matt Cassell looked to me like a serviceable guy who played better than I expected. I saw MUCH more in Jimmy than Cassell during his limited playing time in NE, and I think Jimmy -- while of course still with only limited mileage -- has continued to demonstrate substantially more promise than Cassell ever did. I also think that my perceptions of the relative merits of the two are not unique and that the view of Jimmy's upside is generally a lot higher than Matt's was.
To ElCab's point, I think the very fact that BB is the best in the business is what makes this return curious. We're not at the point when all moves must be good ones precisely because he made them. I don't think he got fleeced either. I do think he could have gotten more than the got, and that remains weird to me.
I think you're looking at this pretty objectively. On the other hand, in the eyes of many of us, we ARE at the point where, if BB made the move, we must presume it to be optimal unless proven otherwise. He takes bets, and not all of them pay off, but his mistakes so rarely cost the team anything material that it'd be harsh indeed to get on his case.
This is obviously a big move, as a 1st-rounder or near-1st-rounder is a major, team-altering asset. But I think you've heard a number of possibilities that answer your question. With the caveat that we'll never know for sure, you need to remember:
- We didn't hear about Cleveland's supposed offer on (say) Nov 4th. We heard about it after Garoppolo set the league on fire down the stretch. Ass-covering, rather than factual statement, should be the presumption.
- Cleveland's front-office turmoil may have made a good deal unlikely to get approved in short order
- Houston looked like a solid mid-table / borderline playoff team at the time of the deadline
- Belichick
hates leaks of things that may not happen, so running a true auction (even among only the 4-5 likely midseason suitors) would be against his nature
- The GMs in the league generally overvalue their first-round picks, because of the PR risks of trading it. Trade it for something less than stellar, even if it was a good bet at the time, and you (the GM) get crucified; merely make a bad pick on draft day, and it's the player gets blamed 2-3 years down the road.
So any of the following are both plausible and would be sufficient to explain things, individually or in combination:
1) None of the other plausible suitors at the time (CLE, ARI, JAX, DEN, MIA) would entertain a topping offer when called upon, and now several are lying to the press and/or their owners
2) Several of the plausible destinations may have been only a good QB away from being a threat to NE (JAX, MIA, BUF), so downstream considerations weighed in
3) BB felt he had a good idea of the other suitors' valuations of Garoppolo based on offseason conversations, that they were lower than what he sought with SF, and as nothing had materially changed with Garoppolo, he could assume those valuations hadn't changed either
4) Garoppolo / Yee had given Belichick a list of teams that he would view favorably for signing a long-term deal with, and SF was on there but others (particularly CLE) were not
5) The old man is getting sentimental and felt Garoppolo could succeed in SF but wouldn't in several other places (Arians retiring, immediate playoff expectations in JAX/DEN, pit of misery in CLE, etc), and felt Garoppolo had given him enough that he deserved a good turn in reply
I'd say all of those are likelier than (6) Belichick did something hastily at the last minute and got taken, or (7) Belichick drastically misread the value of the QB he had been nurturing for 3 years.