I think that most people view these social interactions as an attempt to make the other person feel comfortable (ie that you care about their well-being).

Thus if you change them, you're messing with their heads by making them uncomfortable on exactly the very thing that should be making them more comfortable... thus why it's seen as rude.

yes, you can force them to change on this - but a) you're teaching a pig to sing and b) I think there are more important battles.