@busta level
with radio transmissions the signal/noise ratio is very important.
assuming your receiver circuitry is sufficiently sensitive and it's own noise floor is quite low the only important factor is the SNR of the signal in the air.
so when the ground station transmits with its powerful transmitter the HF signal noise is low compared to the signal thus you get good reception.
but on transmission your effective power for getting signal into the air might be insufficient and the ground station picks up lots of HF noise because it needs to increase gain.
now i don't know if it has to do with the airplane having less metal or the transmitter just being lower power or whatever. but lower effective transmission power might sure be a possible scenario.