With eBay the seller also has to deliver in a timely fashion. You're right, if they fail then the best that happens is you get your money back, but you find out reasonably quickly whether or not they're going to perform, and there's never any confusion about whether or not the transaction has completed.

So a big part of this problem is that StubHub is letting sellers cheat buyers out of massive appreciation by not giving them a reasonably deadline for delivery, nor penalizing the sellers for failing to perform.

The potential costs to correct the situation don't have to be an issue, because StubHub could conceivably push those costs onto the seller trying (and in this case apparently succeeding!) to cheat the system. They could write their seller contract to state that the seller is responsible for all costs borne by StubHub acquiring replacement tickets, and that would remove their incentive to pull stunts like this.