I don't know, but at a random guess, with such immense cargo volume, there could be a danger of implosion during an emergency descent if the hold was unpressuri

I don't know, but at a random guess, with such immense cargo volume, there could be a danger of implosion during an emergency descent if the hold was unpressurized and the inflow rate was not sufficient. It may have been cheaper to pressurize than have rapid inflow.