Reddit's problems started before the recent increase of capability in AI.

It started with all the AMA stuff, then the API BS convinced a lot of people to leave and that was before AI bots were really a thing. In the olden days when moderation was still being done the bots would have been eliminated, via various measures, but now no one cares, and it makes it look like the site is more active than it really is so the admins are not that bothered either.