He is very charismatic.
He is very very talented in everything he do (music, movie,...).
He is here (famous, rich, appreciated) because he worked hard, not by chance.
He is very humble, available,... For example, on TV Show, he is like anybody, he is not like "I'm a star, so I don't laugh, I am here to make some advertising for my movie and that's all"."He laugh, he is close with the public (in a french TV Show, somebody tell him he like the "hello" (I don't know the english word :/) he did with Jazzy jeff in FPOBA, Will stand up and do the ove with the guy. Second example, always in french show, a girl tell him she like him, she love him, and Will stand up to kiss her. Maybe this is not extraordinary, but it is extremely rare)
These are the 4 principals reasons for me !