Ticketmaster has been raising it's rates due to a combination of inflation and post-pandemic demand.

The cost of touring with a band has increased a lot, and many smaller bands just outright refuse to tour right now because it costs too much and they can't justify the ticket prices.

They also adapted a system of Dynamic ticket prices where rates change based on demand much like Hotels or Airlines do. So the more in demand a show, the higher the prices get.

Why aren't competitors undercutting them?

They are trying, but you can't really compete with Ticketmaster

Ticketmaster is a functional monopoly and also controls most of the venues so you can't compete with them. If you do they'll just buy you out or bury you.

Congress is long overdue to step in and enforce anti-trust laws again Ticketmaster