Ticketmaster has exclusive deals with artists and venues. Artists not signing deals with Ticketmaster lose access to venues, and venues not signing exclusivity deals with Ticketmaster lose access to artists. There are enough of these on both sides that neither wants to lose the other so they sign. Side note: I worked at a small ticketing software shop circa the Ticketmaster/LiveNation merger. The CEO got a call from…
Artists can play small venues, venues can book small artists, but that's not where the money is.