It’s not that they can’t, it’s that people are getting blindsided by updates to a game which supposedly hasn’t received updates for over half a decade, and downgrading on Steam is a surprisingly huge PITA. The Midnight Ride recommends patching, fwiw.
Most tutorials I can find involve enabling the steam cli, then using steamdb to look up the “depots” of previous versions and downloading the old update in chunks, then unpacking and copying the old game files to your install location. Not exactly convenient.
No, fortunately enough. A FO5 written by Obsidian could be released as a bug-free superset of FO4, but includes the whole USA and the moddinglinked people would still be trying to mod FO4.
Because the game is old and hasn't been worked on in years. They're no reason to even think about turning off updates for it unless you happen to know the random years later update is coming.
But I learned the hard way awhile ago with Xcom 2. They "update" that all the time, but don't do anything to the game, is just the shitty launcher they keep updating every month.
In my particular case, I just didn’t know it was enabled (my modding guide mentioned a way to stop it, but I guess I did it incorrectly). The game hadn’t received updates in half a decade, and I don’t really use Steam for anything else. Apparently, I wasn’t the only one in that boat.
They can. The issue is it'd eventually split the community. Mods that no longer have support will be lost, and the ones that do will either decide it isn't worth updating each time or have to put up two versions. It also creates needless new work for people, especially the F4SE devs.
Aside from some still holding to LE. There are the 1.5.97 SE users and the 1.6+ AE users. And there have been at least one or two more updates in the 1.6 line that also caused more issues and require their own dedicated builds of various mods.