>Why Airliners Don't Usually Fly At 43,000 Feet Unless Empty
The article never answered the question. There are several reasons (including exposure to radiation)
Surviving a rapid decompression at that altitude becomes problematic for both pilots and passengers… literally have about 5 seconds to get oxygen masks on before the effects of oxygen deprivation; and even if you get your (passenger) oxygen mask on quickly, the chances of permanent brain damage or death are greatly increased, as it takes longer to get down to an altitude with a breathable oxygen level