A lot of it is based on the environment and investment that the existing homeowners have built in the previous decades.
They invested in not only the specific home they bought, but also the neighborhood. They continued investing ever since living there. If they wanted a more dense environment, they would have invested in that sort of location. It costs significantly more to build and maintain less dense-pack areas, from building costs, maintenance costs, to property taxes, and nevermind the emotional investment.
Forced rezoning is to simply declare that:
"Nope, you and your neighbors have made the biggest investment in your life in creating and maintaining your home and local environment, but we want it. You won't even compensate you by buying you out with eminent domain, we're just going to destroy everything you've built and the value of your largest asset by cutting down the trees, paving the grass, and putting up block buildings for all the people that want to live there, destroying the peace and quiet you've paid exorbatant costs and taxes to build and maintain and nevermind the habitat destruction for all the plants & animals either."
It does not work for semi-rural suburbs with 2+ acre zoning, and it doesn't work for quaint San Francisco neighborhoods. I could make more of an argument for the city, since cities are already close to sanitized for wildlife. And, having stopped, for now, a farcical proposal for a high-density building literally in my backyard that would have destroyed a certified endangered species habitat, I can certainly say that it is at best an ignorant prescription.
How is it fair to say that some people built X, we want X, since we can't have it, we'll just take it and destroy it?
More to your point, I can tell you that it is nothing do do with "greedy property owners".
It has to do with having INVESTED in a place and its environmaent, for a specific set of reasons, and having already bought, paid for, and borne the taxes and costs of maintaining that environment, and wanting to preserve that which they have paid for.
If they were actually greedy, they would immediately change the zoning laws to allow all that, as they would EACH make a lot more money from their property, and pay less in taxes. They do NOT make those zoning law changes because they agree that each of them will NOT profit from converting to duplexes/triplexes, etc.
You have it backwards.