Yikes. I see Will's movies have grossed a LOT of money. No surprise his net worth is so high. ($250M+).
From Wikipedia:
Smith has been ranked as the most bankable star worldwide by ForbesAs of 2014, 17 of the 21 films in which he has had leading roles have accumulated worldwide gross earnings of over $100 million each, five taking in over $500 million each in global box office receipts. As of 2016, his films have grossed $7.5 billion at the global box office.