Not that they're not out there, but because how good an actor I no longer matters - as long as they're good-looking and popular, the studios want them - even for roles they're so obviously not fit for!
Then the movie moguls are really stupid. If ditched star power and substituted good acting and writing, they could actually keep more of the profits because they won't have to shell out the money to the movie star hacks. Good films would also better insure a steady audience . If you give people a good movie with good actors na stories, they'll come to the theaters.