Well at least one possible reason is that for live events, the company that has an effective monopoly is Live Nation. And they also own at least one of the platforms where scalpers sell their tickets; Ticketmaster.
I also imagine that as an event promoter, being able to say some variation of "Another sold out show", or "Tickets sold out within seconds" creates pressure for buying early for all future events.
It also takes active planned work to implement these solutions. And if they have a monopoly, they have no incentive to do that work.
It's more profitable and predictable for scalpers to immediately buy all tickets. The ticket seller doesn't care if the tickets are sold to fans that will attend, just that they're sold quickly and reliably and non-refundably. It's even better if tickets are sold to scalpers because some of those tickets might never be resold, which means the venue gets the ticket sale but pays none of the cost a real guest would incur.
What matters is selling the ticket, getting a guest in the door is just expense.
We should make it their problem, by artists not selling tickets on those websites but instead using their own resources. Essentially vertical integration, so then you have to care about the end-product and user experience. And, cherry on top, you might be able to charge more aggressive prices if you're not paying the profit of the middle-man.
That seems to be confusing gross and net margin. When considering a question like “who cares if a ticket buyer ends up showing up?” that’s a marginal consumption question and the gross margin applies.
Why?