>>85424386Because people actually relevant to the anime industry live in Japan and need to take a flight over and find accommodations to be a guest at your convention. If you're not paying them, and not providing accommodations, why would they bother? So you either pay them or foot the bill for their vacation. Both are expensive.
The important thing to understand is that while all cons begin as grassroots events funded and hosted by fans for fans, no big con is like that now. They're run by a cabal of crusty ancient dudes who haven't watched anime since the 80s that run the event as a private for-profit and directly pocket the proceeds to fund their retirement. Expense is the forbidden word, and guest are only brought on when they truly believe it will drive a net profit in ticket sales.
Hence vtubers, who will pay you to make an appearance at your event for the sake of marketing themselves.
