Adverse inflow trap: a new ecosystem gets captured by whoever has nowhere else to go.
You could imagine that OnlyFans was supposed to be a Patreon-style service, that just happened to be erotica-friendly.
Erotica isn't allowed on other similar communities, so those content creators flocked to OnlyFans differentially faster than average content creators.
As a result, the net inflow was structurally disproportionately the most stigmatized use case.
That quickly reduced OnlyFans to "that thing for erotica" which pushed non-erotica brands away.
Another way of putting it: you are downstream of everyone else's moderation policy.
The use case with nowhere else to go arrives at 100%.
You don't get defined by what you allow, you get defined by what you allow that nobody else does.