Dylan Smith wrote:

At 9000' you're flying, the
engine's hot, and you can provide enough heat to prevent the avionics
from going out of spec until a colder temperature.

There are airports higher than that in the States, so I doubt that's the reason.

George Patterson
Love, n.: A form of temporary insanity afflicting the young. It is curable
either by marriage or by removal of the afflicted from the circumstances
under which he incurred the condition. It is sometimes fatal, but more
often to the physician than to the patient.