It's probably a matter of the cops enforcing what they can or what they dare to. Is it easier to bust some 20-something college kid endangering mostly only himself, than it is to go after a well-connected minor local crime boss or industrialist who is illegally poisoning the local environment in a half dozen obvious and fatal ways?

In my own downtown area, I've seen the cops busting old people for riding (very slowly) on the sidewalk, and completely ignoring the BMX kids racing around on the sidewalks, not always dodging pedestrians in time. The reason? It's too much trouble to try to catch those kids; they're too fast. So the intent of the law, making the sidewalks safe for walking, falls to selective enforcement, and cops can still say they're doing their jobs.