IDK man, the more historical Renaissance fairs still exist, with people a bit more strict about dressing period-appropriately. The ones you’re talking about are basically a whole separate thing, it’s basically a fantasy-inspired comic-con, and attracts a whole different audience.
I don’t think there’s anything wrong with either. I think it’s awesome that there’s places for people to sell their niche handmade goods while sporting the fashions of 17th-century France or whatever, as well as places where people can dress up like fantasy creatures, tails and all.