in many polite circumstances people don't want to hear a truth, they want things to go smoothly and easily.
They... kinda are tho. We even have a term specifically for that: "white lie."
Sometimes, like in your "how are you?" example, various patterns of white lie ossify into social protocol where both participants are saying things they don't literally mean, but both participants know the game.
You've probably heard of cases where anglosphere people go traveling, ask people how they are (or use any of our other non-literal pleasantries), and are surprised when a real answer is given.
This is exactly how many people outside of US feel when they observe the customary American greeting exchange of "How are you?" / "I'm fine, thanks." when it's patently obvious that the person asking doesn't actually expect any other response even though the person responding is obviously not fine.
Like, we get that this is a cultural thing and that it would be wrong to ascribe some profound meaning to such individual interactions. At the same time, it does make the overall culture look bad when that sort of thing is expected and even enforced.