When my state first imposed mandatory use of seat belts in cars, the public was assured that "this will not be enforced as a primary offense, only secondary if you are already violating some other law e.g. speeding, expired plates, etc."

Well that caveat was not actually written in the law, and enforcement changed later. Now you can be pulled over and fined for nothing other than not wearing a seat belt.

So whatever "they say" about enforcement is meaningless. You can only consider what is actually written in the law.