Why would Shanahan let him get away?

After missing 12 games in 2021 with a torn quadriceps, McGlinchey started every game for the 49ers last season and posted the second-best pass block win rate of his career (89.6%) and a career-best 81.3% run block win rate, which ranked fifth overall among all tackles. He is a strong edge blocker who wins with angles and his ability to get off the ball, and he has the lower-body flexibility to match speed off the edge.

Priority position is d line

Will try to draft and develop o line

He's a middle of the pack pass blocker

and an elite run blocker. For whatever reason he has taken a lot of flack from the fan base. As if he alone is the reason that they were not great at pass blocking. I think the 49ers will miss him quite a bit more than they realize when that edge does not get sealed.

His pass block success was 32nd among tackles.

Not sure the niners wanted to pay top dollar for a middle of the pack pass blocker.

Perhaps salary cap issues?

Quick google indicates SF has only $5.7 of available space and ranks 25/32 overall. Many teams are having to make choices these days.

Or perhaps McGlinchey wanted to move on?

Likely. Niners just signed Javon Hargrave for 4 years

$84 million.