It’s mentioned in this really good Verge article about SEO. I don’t think it’s a good sign for Reddit to just allow such blatant spam and makes me think how much subtler spam is out there too.
I’ve personally noticed more a few times in old threads you’ll find a comment made months later that’s recommending a product.
I think many people will migrate off Reddit as the discussions become increasingly synthetic. I’m sure plenty will stay but I hope enough leave so alternatives can improve.