>What boggles my mind is that they didn't
>start diverting flights to other airports

I'm not sure what the costs are to land at somewhere like DEN, but I assume landing a fully-loaded A320 is in the thousands (if not tens-of-thousands) of dollars. Also, keep in mind all the luggage would have to come off, get picked up, then get put back on again.

So imagine a flight was diverted to somewhere like DEN so people could clear customs:

- Plane lands at great cost to airline
- Everyone gets off plane and gets luggage and clears customs
- Everyone checks back in again to get boarding passes to get through security
- Everyone reboards

A logistical nightmare.