I'm curious why that's never caused legal trouble for them. They have a dominant position in the ticket-sale business, and companies with market dominance like that usually aren't allowed to try to extend or defend it with exclusivity agreements. Microsoft and Intel both got in trouble for exclusivity agreements with OEMs, for example.
There have been congressional hearings regarding Ticketmaster's monopoly. Not sure why nothing came out of them.
Now with the live nation merger they own the venues!