There is actually a ton of this.

There is a huge Bay Area... not sure what to call it - public/private charity? - called the Peninsula Open Space Land Trust, that has a huge amount of donated land in the Silicon Valley, and is a very popular charity with very deep pockets that can buy land to basically turn into parkland.

They have over $300 million in assets and own over 97,000 acres, and have partnerships with quasi-governmental agencys like the Mid-Peninsula Regional Open Space District to administer those lands as parkland.

The idea that noone is doing this is bullshit, and the idea that it is only done as a tax break is also bullshit.

This organization is a leading reason why living in the Bay Area is valuable and isn't complete urban sprawl. I wouldn't be willing to pay Bay Area prices if not for the existance of the land preserved through organizations like this.

https://openspacetrust.org/ https://www.openspace.org/