It became a niche segment in the real estate. The idea is you find land that is cheap, but you have a feeling it has mineral wealth. You buy it cheap, get the survey done, and show that it was really worth a lot more. But instead of building a mine/oil well, you declare the land undeveloped for perpetuity. The tax benefit you receive is commensurate to the (now highly increased) value of the land.
You make a profit this way, and the environment benefits.
It's a very risky part of real estate. There are lots of environmental groups who closely monitor the land, and will file a lawsuit if they suspect you are developing on the land. Fighting lawsuits is part of the risk.
Anyway, the person who did the presentation showed some interesting statistics. Supposedly, for every 10 acres of land that is developed in a given year, roughly 9 acres are declared undevelopable for perpetuity. That's really significant (if true).
The only way I can think of to preserve the wilderness without any isolated homes for the wealthy is for the government to buy up the land. I'd probably support that, if we could get it done, but it does mean that if the money for it comes out of the general fund, then you probably have average people paying for more of it, instead of mostly the wealthy.
This is also a massive problem in BC; the ALR exists to do exactly this. There's lots of land available, it's just illegal to build anything other than a farm on it, and the real estate market is as a consequence as usurious as you'd expect it to be.
Of course, none of this is new. Enclosure predates the Romans.