Because you don't know if people are doing this or not. Its not easy to spot someone who is non-compliant. But it is a helluva lot more effective. Like, no comparison.
Right. So if we were serious about SCIENCE we would mandate hand sanitizer everywhere. People use it when they see it. People don't when they don't. This would stop the spread of the virus a hell of a lot more than masks. Both should be used. But masks seem to be the thing that everyone has up their ass, so its about masks. Not science.