75,000 tickets x 300 per ticket (it's a little more, but let's just call it 300 for fun) = 22.5 million dollars. Let's say The Rolling Stones cost 9 million--a ludicrous figure, but I'm doing everything I can to help your logic.
1 weekend: Coachella nets 13.5 million.
But with 2 weekends, you're right, watch! They make 22.5 million twice so 45 million...
and then they... have to pay the Rolling Stones 18 million..
and somehow Coachella makes 27 million.
WHOA, THAT'S CRAZY! HOW DID THEY END UP MAKING MORE MONEY?!