There actually is some research that shows masks are somewhat useful — better than none anyway — for helping stop airborne particles.
One (limited) study:
https://www.sciencedirect.com/scienc...95670113000698
There’s a bit of a trust problem in telling the population not to bother with masks because they don’t work, then saying medical workers need them badly. If they don’t work why would they bother? Because the baseline often being cited against cotton based face masks is N95. But against no coverage there’s some obvious benefits (like not touching your face) and some evidence showing it protects. That’s why medical staff need them.

