Idk about the others but in VRChat it's animes and furries who don't compress/resize textures and same with worlds.

At least VRC lets you define max cache size and it generally respects it.

My uneducated guess is that those are from custom stuff found on the servers you visit. Quake 3 and similars (Jedi Outcast/Academy, Unreal Tournament 99/2004) would download any custom maps, player models and skins if the server you were connecting to had any.