To be fair, there is a smell, albeit a more subtle one than full decomposition, right after death. I’m not talking about excrement, I’m talking about the other smell. When a body dies, think of it not just as a release of the bowels but everything else as well. Cellular release begins such that kissing a corpse goodbye, on the forehead, as often takes place in movies and such, would also be taking on a corpse-y bacterial load. Viral if otherwise infected. In the most benign sense, probably just staph In the unrefridgerated, small enclosed space of a plane you’re going to want to get the corpse hauled off asap.

Not the best article to convey this breakdown, but it illustrates the potential here.

https://www.sciencedirect.com/science/article/abs/pii/S0360132325006419