Instead most of these parks have fences around the grass, and you're not allowed to lie down there and hang out. Some are also "temples" and have guards that'll yell at you if you even sit down out of the way on some stairs for a second.
I live in Amsterdam, and in general I'd much prefer living in a smaller house with no yard of my own if there's a big park nearby, but in Japan I'm not so sure. If I can't use the park for anything worthwhile (lie in the sun, have a BBQ etc.) I'd rather just live in an American-style suburb with my own small yard.