The money is the economic incentive. The points resulting in license suspension fills the other loophole.
> Once in a while, I get a ticket for it. I just pay it and continue not having a license plate on the front of that car
Yes, I agree - your state shouldn't have this loophole. Since the economic penalty doesn't work, you should also be receiving non-monetary penalties for this behaviour that would have resulted in revocation of your driving permit (and further violations would be criminal).
> Once in a while, I get a ticket for it. I just pay it and continue not having a license plate on the front of that car
Yes, I agree - your state shouldn't have this loophole. Since the economic penalty doesn't work, you should also be receiving non-monetary penalties for this behaviour that would have resulted in revocation of your driving permit (and further violations would be criminal).