How do the other presets work?

In Gacha life past page 10 of the presets there’s more with a different background and they look fanmade. In Gacha club (depending on the club or whatever) once you go past the first page of it they all look fanmade. And in Gacha life 2 the presets have usernames under them indicating they’re fan made (besides the official ones)

So how does this actually work though? Are they all semi popular gachatubers or did they submit their characters in and they got put in the game?