I think that's where the "reputation laundering" angle comes into play. With its unique position, Ticketmaster gives artists plausible deniability. "Nothing we can do about it", "evils of capitalism", "a monopolist captured the market, government doing nothing", etc. - say artists, for whom the image they project is a core part of their market value. With a properly functioning competitive market, those same artists would have to either get much less, or answer some inconvenient question about ticket pricing.