The people that live in those area, and own those deeds, are the ones that vote and or convey their desires to their representative to impact the rules in those areas.
So I guess the answer to your question is "because those people bought their deeds under when a certain set of rules were in place, and they are in a position to exert pressure to keep those rules in place". Why would you expect them to act against (what they perceive as) their own self interest?
The answer of "because it helps society as a whole" is a powerful one, but not one that holds enough weight for a lot of people to give up a significant portion of their net wealth / retirement / satisfaction.