it's payback for all the time you did it to them when you jump out of your car for a mission and just leave your own car on the street blocking traffic. if you take the time to seeking out the 5 empty parking spots in the whole of night city that is located 2 kliks away from your current position and actually park in the designated parking spots, they will also stop doing it to you as well
personally, i'd just summon my caliburn and push them out of the way or summon my akira bike and go around them
moral of the story... it's a game
dont believe me? go play the mission burning desire or the Sinnerman quest.