Bowling for Columbine was the highest grossing ‘documentary’ of all time upon release. And F 9/11 replaced it. It’s not a lot of money but considering that his films are archival clips intercut with him walking around in a baseball cap it doesn’t take a lot of money to make a profit.
You and I have a different definition of a lot of money. Bowling for Columbine made 27 million in the US. Fahrenheit 911 grossed 221 million world wide and 119 million in the US alone. That, to me is a lot of money.