There's also a perception (and realistic) issue, of there being more ways to win/lose and pull a miracle, come from behind victory in MMA. So corners become hesitant as we have seen many times a guy pull a hail mary technique and manage to catch the opponent off guard and win.
Where as in boxing, if one guy is simply better then that's pretty much that. Boxing has a long history, and ring control within the sport is a literal science at this point. So being the much better boxer and getting caught with something wild is amateurish (and becomes increasingly unlikely at the higher levels).