SO was already well DeadOverflow way before LLMs were a thing. For reasons people explained when SO came out: just as FaceBook was bound to be filled with accounts of dead persons (earning it the name "DeadBook"), SO was bound to be filled with outdated answers. That the people asking the question could pick what was, according to him, the proper answer was a huge mistake and it's been immediately pointed out as stupid and they didn't fix it: not only wrong answers were picked, but also answers bound to be soon outdated were picked as "correct" too.
Don't get me wrong: I used SO a lot in the beginning, but the problems --that many foresaw-- quickly became obvious.
And I'm not saying not allowing to pick one correct answer would have saved SO: but its downfall probably wouldn't have been so abrupt.
Not all is rosy with LLMs but at least we don't have to suffer SO answers and SO comments anymore.