Why would Tom Cruise want to be 007? He is famous enough. He cannot become more famous being 007 and 007 will not be more popular because of Cruise.
It makes sense for the owners of the 007 franchise to cast a relative unknown such as Pierce Bosnan and Daniel Craig as they will be relatively cheaper. When they become more famous and start demanding more money, dump them and "restart" the series.
This is the reason why the superheroes are almost always played by unknowns. Spiderman by whathisname, Superman by whathisname, Batman by Christian Bale (relatively cheap).
A well-known star is casted to drive a movie not the other way round.