Any idea why this happens?
Looks like someone has paid to have bots spam that particular coin on this forum...
That might be true for the first screenshot in OP where the bot account talks about sushi, but in the other examples, they talk about bitcoin and the supply of money. I don't see an incentive there.
Two possible reasons:
1. They are trying to farm accounts by getting the required activity levels up and possibly getting a few merits here and there.
2. Their ultimate goal is to spam a website/service, but they are starting out slowly with a few generic posts to avoid getting reported and nuked straight away.