Two reasons why bins are left on the curbs.  One is to prevent vehicles from partially blocking or even blocking their driveway (need to leave 4 feet of clearance from driveways but is not enforced).  And the other reason is there is no room to place their bin as the curbing is full of cars.  What do you do then?  Put it on the street and block traffic?  Maybe each household should have an area reserved for bin pickup but I know that won't happen as finding street parking is a problem in many neighborhoods.