I guess they linked germs to bad smells (e.g. miasma) and figured out good smells might counter them. It's a pity they hadn't invented essential oils at the time.
Who was advocating for leaving your nose out? We used to make fun of the morons we saw doing that.
Frankly, I’m sad masks aren’t still more of a thing. I don’t want to wear one all the time, but if you’re sick and need to be in a public place, throw one on out of consideration for your peers.