31 mph is not too bad, but at higher speeds you start facing safety risks and instabilities of different kinds besides just falling over. Going downhill very fast on a road bike is not a super stable configuration. You can slip on turns, lose control on bumps, hit something you didn’t have reaction time for, etc.

I think planes have this too where they’re safer at higher altitudes, except not too high beyond what they’re rated for and have other instabilities from that