It makes sense for those who are big enough in the Game Industry (which is now several times the size of the Movie Industry in terms of revenue) to try and do the same as movies and leverage that sweet brand recognition of celebrity actors to sell more copies of the game.

However I suspect it doesn't work quite the same in practice as the "main character in the story" in games is almost invariably the player him/herself and those famous names will never be more than secondary characters with limited interaction possibilities.