They don't just ban subs randomly for the most part, they've slowly been changing reddit rules to make the site more advertiser friendly. So yeah, most of the below broke reddit rules, but not when they were created, they got banned shortly or immediately after a rules change, AFAIK. I think /r/thefappening was banned without a rule change, and I'm not sure what rule it broke at the time.

/r/nflstreams, /r/gundeals, /r/gunsforsale, /r/shoplifting, /r/thefappening, /r/darknetmarkets, /r/deepfakes