Well, speaking for myself, I can't think of a single instance where I've worn them in public. Although I have to admit, the aesthetic and hygienic reasons you listed had never occurred to me. I mainly would fail to wear flip-flops in public because I'd be paranoid about stubbing my toe or accidentally cutting my foot against a sharp edge (yes, I'm neurodiverse).

The only times I've worn flip-flops outside of my house have been:

-- in my backyard, frontyard, or driveway...literally when going to get the mail, relaxing on the patio, or momentarily going out to throw something in the compost

-- in the locker room at the gym, when using the public showers or the sauna

-- at pool parties (but usually these were pool parties attended almost exclusively by gay & bisexual men)

In fact, if I encountered another man (or a woman) wearing flip-flops in a public venue, I'd probably be too busy consciously making sure I'm AVOIDING stepping on their toes (literally) to even notice their grooming habits. :-P