Please also take a look at this, which I think explains the situation well: https://wiki.openstreetmap.org/wiki/United_States/Public_lands

"In particular, leisure=park is widely misused on areas more properly tagged with boundary=protected_area or leisure=nature_reserve. OSM's leisure=park tag (a smaller, manicured, urban park) conflicts with "park" as used in US English to mean "a large area of land kept in its natural state for public recreational use.""