Most likely because if you parked on a parkway you would most likely get hit, and if you attempted to drive in a driveway, you really would not get very far.
Have you even BOTHERED to look at the Related Questions at the bottom of this page to see how many times this has been asked?....B O R I N G! ZZZZZzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz
no i didn't know i could do that thanks the heads up. i just started q&a two days ago. I'm still learning
I always thought that was silly.