1. Context matters. That question is rarely asked by anyone that isn’t a douchebag trying to hit on a woman.
2. From my understanding, even when NOT in the context of douchebaggery, it’s a condescending thing to say to a woman. So much of society wants to put women in a box where they’re expected to look pretty, smile more, talk less, and listen to big strong men with their big manly brains. Being told to “smile more” is pretty triggering for some (but maybe not all) women who are tired of dealing with that shit.

Disclaimer: am man, as my username implies.