Their moat is a combination of vertical integration(their parent company owns a bunch of venues) and contract lockup with other venues they don't own.

Also, since artists make almost all of their money from tours, they know trouble will arise with the mess that is ticket/venue sales. If they go full capitalist and someone like Taylor Swift starts charging what the market will bear(maybe $10k/ticket ?), many people will revolt, since there is zero chance they can afford that.

Instead, they can lay 100% of the blame on Ticketmaster, and nobody hates the artists for the mess.

So artists are not incentivized to try and fix the mess, and venues are not really incentivized either, since they also get to lay the blame on Ticketmaster.

Ticketmaster in the meantime takes all the blame, does nothing and keeps depositing fat stacks of cash in their bank account.

Some incentive will have to change, for this to get fixed. Perhaps govt will slap some regulations on Ticketmaster? Perhaps people will stop blaming Ticketmaster and make venues and/or artists accountable for their continued contracting with Ticketmaster? I don't know, but until something changes, don't expect Ticketmaster to behave or a competitor to show up.