Why are there son many italian american in the US show business and government?

I'm not from the US but it seems to me like there are so many italian american. So many actors and actresses have italian names (leonardo di caprio, de niro...) and thas is true also for the music industry as there are like Lady gaga, madonna and so on..... I can see a lot of italian on the telly as well...(the woman on regis and kelly, jay leno..) . They occupy quite high position that the chinese, mexicans and others cant even dream of..