I've always wondered if human nature wasn't to blame for this....
Think of how we've been taught and conditioned to drive a vehicle normally. When you are moving, one feels free to move along and use the road as you see fit. But if you have to stop or pullover, the courteous thing to do is get off on the side of the road, so traffic behind can pass thru safely.
Now I know its not a road, and its a different situation being on the course, but I'm guessing this happens subconsciously, especially when our mind also subconsciously recognizes how most cart paths are only little more than 1 cart wide.
hence the curbs are needed near tee boxes and greens to prevent this programming from taking over...
Just a thought...