In all fairness, airplane food was famously tasteless and subpar, so much so that inquiring about its "deal" remains one of Jerry Seinfeld's most famous jokes. Mind you, the question isn't actually about airplane food. It's more about ripping on the audience's common enemy, which is no different from asking: "Boy, that Hitler, what a character, right?"
Airline food tastes the way it does due to the plane's environmental factors playing the fandango on your senses with a baseball bat.
Modern planes travel at an altitude of about 35,000 feet, which, in terms of places most likely to kill you, ranks somewhere between the foot of an active volcano and inside the wife of an angry lumberjack who unexpectedly came back home for lunch. That's why airplanes have to keep the cabin artificially pressurized -- to keep your brain from swelling and leaking out of your ears. The problem is that, according to modern research, the cabin's pressurization combined with the plane's white noise can numb your taste buds, suppressing your ability to taste salt and sugar in non-fatal doses.
"Oh, so that's why my overcooked circus elephant tasted a bit weird!"