I think it’s likely a combination of bots made to generate “engagement” and bots trying to establish themselves as actual users so it becomes harder to spot them pushing a scam later. Content creators may pay for bots to comment to help their videos get promoted, or an enterprising individual may make a bot army to comment on a specific video and try to then sell their engagement services when that video does better. YouTube also has an algorithm for banning/shadow banning accounts pushing scams, leaving “normal” comments may make it harder for YouTube’s algorithm to spot these people.