For the most part, they are getting what their contracts said they would get. The comics industry is well known for taking ownership of everything an artist creates for them. Like actors getting screwed over because streaming wasn't covered in their contracts back when they signed on for previous movies, some comics artists are still stuck with the old contractual agreements. If the contract requires renegotiation in order for them to get a cut of the proceeds, it's 100% up to them to fight for it. Licensing and IP ownership can be convoluted and messy.