Gumroad wise i see the issue as its not advertised.
People only look quickly and your models were not categorized as being vrchat ready
most avis that get vrc ports have VRC in the title which makes it visible when people search for VRC models.
people also are lazy and often will skip pages if its not on the the actual title
not to mention i dont see even on your gumroad that a model is listed as vrc in its info, any preview images or info on what it contains and that will impact sales heavily
A little bit of advertising, making the title for the avi contain VRCHAT, including images of the vrc port and such can go a long way to grab attention and sales. Maybe try that with existing ones and see if that changes?
would defo recommend looking at how popular avis structure their avi pages with its info :3