This is uninteresting. You'll find these aren't variations in policy by National across locations - they reflect different taxing authorities at the airports: state, city, county, airport authority, stadium funding, common rental area, etc.

The first incident I can recall was a misc daily charge at ORD. Your outrage is coming nearly three decades late.

If you checked National LGA and Avis LGA you would likely find significant equivalence.

As such, this isn't a National problem, it's OMNI. There's a forum for that.