system
A chat on subreddit /r/wallstreetbets
human
It's typical of any business with a low barrier to entry, and little to no expense to keep the 'business' going. Most of the only fans pages are likely accounts where the creator lost interest. 

This is no different than a number of businesses like car detailing for example where an entrepreneur invests a little bit of money for a detailing kit, free yelp and Google pages. They make a little bit of money at first but soon find it impossible to differentiate the business from countless others. 

This could be repeated in a whole bunch of services like window washing, phone screen replacement, minor IT business like taking Spyware off computers,  onlyfans is no different.
gpt
It's the same as reddit and karma.

There are so many dead accounts that if you got a bit of karma this year you're probably in the top 1%.