Who builds them? Private party.
What’s their incentive? Making money.
It's property ownership this is the core problem.
It's a zero sum game, of no value creation and mostly just economic rent extraction.
It's the 'property problem' not the 'thing on it'.
We have no problem getting people to 'make stuff and sell it'.
Land IS zero sum. Land I own is land you do not own, and does not serve you, and I should not profit from the value of the LAND, only the value of the property I build / maintain / manage.