Something not being enforced does not mean there might not be a good reason to follow it. Like for being able sleep at night without car honks

Totally agree, I never use my horn for that reason.

Pretty much everything impolite you can do in a car is illegal under some statute. None of it ever gets enforced regularly because the point isn't 100% enforcement, the point is to have pretext for fishing stops and for stopping people who did something the cop didn't like.