This happens in many industries. The venue knows they are in the position to deny access to vendors. A tame captive crew is ripe for taxation.
On the other hand the vendor is free to add to his quote for a taxing venue. The venue has to be extra good to make up for the inflated prices being charged.
The venue banks on them being the best so the best vendors are happy to charge a bit more or eat the tax on their significant fee to get in. If neither is true they wind up with 2nd or 3rd tier vendors and their own status falls.
This naturally favours monopoly venues such as stadiums, airports, destinations, and the big in demand function venues.