Laws are
always selectively enforced. You cannot simply watch every citizen 24 hours a day, and you don't want that kind of society in the first place.
What you don't want is there to be some pattern to the selectiveness. Certainly not due to corruption (the enforcers turning a blind eye to some select individuals), but even if there is no such corruption, the patterns are hard to avoid.
Just because people figure out that they can get away with something doesn't mean it shouldn't be a law. There may be reasons why it shouldn't, entirely unrelated to the popularity of breaking it.
Even if generally enforcing a law seems hopeless, if the law is in place, it can be used in certain situations. Like dog poop. A neighborhood having problems with a particular offender can lean on that law to get something done about them, even if there is no enforcing to help with someone randomly bringing their dog (e.g. by car) from another neighborhood to have a poop.
Where I live, streets have an implicit 3 hour parking rule. Street segments which have no signage about parking, and are available for that purpose, essentially have an implicit, invisible "Parking 3H Max" sign.
Nobody will actively enforce it; you can park your broken down old van in front of someone's front yard and leave it there for months. If nobody calls to complain, likely nothing will happen to that vehicle.
The law exists there for complaints; you can lean on that.
You can also lean on it in situations like this: you shoveled deep snow for an hour and a half in front of your house to dig your car out and create a clean parking spot. When you come back from your errand, your dickhead neighbor, or someone else, has parked there. If they stay for 3 hours, you can have them removed.
That's the concept you're missing; laws do not have to patrolled by active policing that looks for infractions. Enforcement can be complaint-driven. If you repeal a law that is often broken without causing a problem, you take away the basis for someone to have an actionable complaint in those situations when it does cause a problem.