I think another factor is how the Sox determine a player's value, and they seem very firm on whatever amount they come up with. We see it happen with some FAs, where our offer seems way lower, and there was no evidence we ever move beyond the initial offer on many. The Soto talks seemed different, but we are not even sure what sort of offers we made or increased.
I think we feel like we know the precise value of our own players, and it often seems low. We don't seem to budge and often come across as stubborn and ungrateful. We have seen a lot of really good players walk as FAs, and to be honest, I think we have gotten more right than wrong, in terms of knowing when to "move on."
We missed on a few, and some did well (Beltran, Lowe...), after leaving, but maybe was still not a mistake (Damon?) We have also traded some big names away, just in time: Nomar, Manny, while others were just last ditch efforts to get some value back (Lester, Lackey, A Miller) or tag ons to salary dumps (AGon and Beckett tied to Crawford.)