I like the question, but I don't think I have the answer.
I've actually heard my snoring, but that was when I was either drifting into sleep or gradually coming out of it. Not a pretty sound!
But I guess it's because sleep is overpowering, we need it. There's gotta be physical reasons why our bodies require sleep, our bodies eventually shut down if we are totally deprived of it. Plus, I'm told that while we sometimes can delay sleep, in actuality we can't prevent it. Sooner or later, our bodies shut down. Sometimes there is warning, sometimes not. I've met a couple of people who before being diagnosed with sleep apnea had auto accidents, and they simply snapped into sleep, with no warning of it whatsoever. Some of us can feel the drowsiness come on, but they didn't. I suspect all our abilities to deal with sounds, sights, and more are suppressed by sleep. Warnings, delays, whatever.... eventually your body requires sleep, and no amount of noise on your part can prevent it.
However, it seems we sure can keep other people from sleeping!
I think that despite all the research done on sleep, it is still largely a mystery.