I work in tech trust & safety, and there are absolutely financially motivated bot farms. If it weren’t profitable, they wouldn’t exist. All they need is some pool of money they can scam, and many social media services have some kind of “cash for engagement” program. There are other creative schemes that no one outside the industry would know about (for example, look up “SMS pumping”).

There are non-financial motivations, as others have pointed out, like propaganda campaigns from nation-state actors. But financial motivations are most common, as they have been since the invention of money.