It's called bad planning.
When I was a young adult there we're no buildings on the southeast corner at YMEN and no freeway or tollway. The Moonee Ponds Creek was a creek. And then Governments looked at the "unused" land and encroachment began.
Back then, YMBN was a grass all-over field surrounded by market gardens and the odd dairy farm. And planners in Councils and then the Commonwealth saw the "empty" land and encroachment began.
At my home town, YSHT was outside the town boundary and there were opportunities to purchase adjoining farmland to extend the main and cross-strip runways. But the Council and the developers (funny that) saw the vacant land and it was subdivided. There are now houses and factories up against the aerodrome boundary and the Council and some of the bright business people are talking about a new and bigger airport further out so that bigger aircraft can operate. Of course those of us who fly from there now will never be able to afdord the cost-recovery rates and other charges that will be levied so little GA will become even littler all over again.
I ask myself the rhetorical question "who has made a lot of money out of all this, and what influence do they have to achieve it?"
Kaz