One detail I haven’t seen in other comments. In the uk at least, live nation / Ticketmaster will sign exclusive deals with artists - limiting them to a summer

One detail I haven’t seen in other comments. In the uk at least, live nation / Ticketmaster will sign exclusive deals with artists - limiting them to a summer run of (for eg) five live nation festivals and no performances at any non live nation events. So even if alternative venues / festivals exist, live nation squeezes them out by being able to sign bigger multi venue/event deals.