If it gets zoned as parkland as part of a sale - great! You should be able to make that part of a sale contract. But if the governing body then votes to make it something else a decade later, that should simply be part of how things work.
Old people ossifying things to how they prefer via preventing future generations to freely operate is not how I want a society to run. If anything the older you get the less say in the future you should have.
I see plenty of people here angry when the idea is floated of the US government opening up public land for mining, drilling, etc. You may not be one of them obviously, but how is this different?
What do you think the outcome of this would actually be?
Someone wants to sell land to develop a parkland but they aren't allowed to dictate that it must be a parkland.
So they just don't sell it ever. Now instead of a nice park it's a direlect lot for decades
The answer to this problem isn't "fuck you old people we're taking your land and building data centers"