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
To add being the internet you just have to straight up be lucky the algorithm chooses your content out the pile to display, think of all the YouTube channels with dozens of videos for a few hundred views