I think it’s based on two things: where you are and how the letters start when written.
When writing letters n and U, both are started at their leftmost position (for most people) and their topmost position (for most people).
In the UK, or other places where you drive on the left, a u-turn would make a little n. While you aren’t starting the turn from the topmost position of the letter, you are starting on the left of the letter.
In the US and other countries where you drive on the right, you make a U-turn because viewed from above you are making a U that starts from the top and left of the letter. While from your immediate perspective while driving your making a lowercase n but starting from the right, from above it’s the classic U movement that occurs.
I think it’s based on two things: where you are and how the letters start when written.
When writing letters n and U, both are started at their leftmost position (for most people) and their topmost position (for most people).
In the UK, or other places where you drive on the left, a u-turn would make a little n. While you aren’t starting the turn from the topmost position of the letter, you are starting on the left of the letter.
In the US and other countries where you drive on the right, you make a U-turn because viewed from above you are making a U that starts from the top and left of the letter. While from your immediate perspective while driving your making a lowercase n but starting from the right, from above it’s the classic U movement that occurs.
Just a guess though.