Well, plus, practically speaking, it just paints them into a corner with invincible plot armor. As it is, the only Avengers that Thanos actually killed before Snapageddon were the 2 he got the stones from. If they all come back in a snap reversal, you basically have the most powerful being in the universe, with all 6 infinity stones, unable to kill anyone of note. Where do you go with that from there? Who could ever be a threat again? And we already have semi-spoilers, because there’s a new Spider Man coming, and right now the GotG consist of...Rocket. So at least some are coming back somehow.