^ This.

~15 years ago, I was working with venues to see how we could handle ticketing, etc. They ALL had exclusive deals where the venue could ONLY sell online through TicketMaster and then TM would handle ~100% of the back office reporting, tracking, etc and even the onsite credit card processing for walk up sales.

It was one end to end system/suite and to replace any of it, you had to replace ALL of it once the contract was up. Not a fun space at all.