The problem here is that getting one's money back doesn't feel like enough, because you're losing out on massive appreciation of the purchase between when you bought it and now.

This is one of the most difficult customer service issues to solve, because the cost to correct the situation in the customer's eyes has no upper bound.

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.