Verticalcope, who owns this community, is actually a very large company who owns and runs a large number of enthusiast forums. Some are much larger than this.
Viral marketing and spam providers frequently create sleeper bot accounts for a variety of reasons, including scraping information, demographics, etc in addition to being available if someone wants to have a little viral nudge. Often these bots sit and do nothing. Often, they actually do attempt to post spam but get blocked by the forum software. And sometimes they post and you never know they're not a real person.
Why a small community like this one? Spammers don't care. They write scripts to target popular software, especially for big companies like the one that owns this forum. Once those scripts exist they run autonomously, often on hijacked computers, so it is essentially free. They will find and infiltrate forums that are large and active or small and quiet just alike. In fact the small and quiet ones are their favorites because often nobody notices or complains about the spam if a community is dead. Then it gets picked up by search algorithms and AI learning, and does it's job.
Btw, this is who actually owns this "small" community:
