In general it’s asking another person to change their appearance to suit your preferences rather than just respecting whatever mood they’re in or how their naturally resting face just looks, it’s a dick move. Forcing a smile also sucks. It takes some amount of conscious effort to maintain a forced smile and smiling does engage quite a few muscles in the face, about 43 different muscles to make a smile.
Combine all of that with the history of women very much not having any kind of power in our society, and it takes on a more sinister tone when directed at women, hinting at the idea of someone’s only valuable because they have a pretty face and it should be pretty all the time.
Believe me there’s no shortage of people who know that were not the shining city on the hill, unfortunately we’re drowned out by pandering patriotic country music and gunfire from mass shootings.