Overall there is a simple answer to this question:
Why would people like the VF cast more than the characters of their own game. I play DOA to play as DOA characters. The VF games inspired DOA, that's why they are in DOA. They are respectable guest characters, and probably the best guest characters I've ever seen in a fighting game. But I play DOA for DOA, and as a character loyalist I wouldn't wanna worry about my character making it to the next game.