Many of the other commenters have explained how the ownership structure of Ticketmaster gives them near monopoly control because they also own the radio stations and the venues and the promoters. (I'm using "they" and "own" very liberally in this paragraph.)

The simple fact that there's an ownership link between Ticketmaster and the scalper I mean totally legit resale sites is so wildly corrupt that, well, it's textbook stuff.

What I haven't really seen discussed in the comments is that the role and objective of Ticketmaster is poorly understood. They seem like the people who sell tickets, but in reality they are "blast shield for consumer rage" as a service. Their role is to industrialize the conversion of anger into waste heat while leaving the musicians looking like neutral parties.

They also do a lot of catch-and-kill; once competitors get too big, they use bully tactics to starve them until they can acquire them cheaply.

There's an app called DICE. I like it a lot. I'm rooting for them.