It's almost always bot accounts. Reddit is decent at catching bots so the botters copy legitimate comments, build a post history, and then switch to scamming or spamming after the account has some credibility.
Totally possible. Maybe enough people figured out how to game their detection so they gave up, or if it was so gameable in the first place it was never as good as I'm remembering.
I don't know about that so much. I'm seeing a lot more straight up spam on reddit that looks easy to spot, but I think reddit gave up or something...