A lot of these tickets get resold on the platforms themselves. If a reseller buys the ticket, and then sells it again to the end user, Ticketmaster gets paid twice.
This point results in at least hundreds of millions in revenue. Now, if one of the platforms “cracks down” and makes it harder to buy and sell people will prefer another platform.
So platforms have a huge disincentive to do anything about resellers.
Also…more obviously, demand pressure drives the price, so scalpers are helping create a market and getting paid for it.