designing original RPs takes more work than building on a fandom, as you have to set up everything. That alone is the core reason you see fewer original RP worlds. There are a few here and there, but most find it easier to take another world and tweaking it or building a scene within it.

It is undeniable that proper worldbuilding can and is fun, but it does also consume more GM resources.

thus in our opinion, the balance between fandom & OC RPs being what it is isn't a problem, its a plain fact. More people prefer easy setttings to deal with than the complex stuff. That permits them to be creative with their character(s) and their IC posts, rather than to have to expend a major portion of their available creativity on crafting a role/setting for their character.