Ok this is going to sound silly, and I apologize if this isn't a nice contribution.

But I believe to have read quite a while back that H2S is why poop stinks so bad for us. It can lead to anoxic events: https://en.wikipedia.org/wiki/Permian%E2%80%93Triassic_extin...

So evolutionary speaking we might have adjusted our olfactory sense to stay clear of any H2S sources.