Risk/reward problem - circle to land in tight mountain valley or land with 30 kt tailwind.
Circling at Aspen isn't an option in the Challenger; airport max speed for circling 140 kts (very strictly enforced by the granite), Challenger min speed for circling 150 kts.
Max tailwind 10kts, so they shouldn't have been even thinking about it.
As for the landing flaps 20 suggestion, apart from the valid legal point made by MfS there is so little drag that the aircraft struggles to stabilise at Vref on a 3.5 degree slope, let alone 6.5. It is worrying that someone even thought about it.
