What is the difference between the current American urban planning system where certain property is restricted to certain purposes and eg developers must devote

What is the difference between the current American urban planning system where certain property is restricted to certain purposes and eg developers must devote certain amounts of land to parking lots and the proposal of the GP where some land must be devoted to certain “green space”? (FWIW I mostly disagree and think the city or some trust should just own that green space.) It seems to me like you’re ranting against the status quo and not anything particular about the parent comment.