What they tend to do instead, though, is build things like rooftop gardens on top of office buildings. While these areas are technically open to the public, it might not be easy explaining that to the doorman who has never heard of any such thing. And how would you know it even existed if you weren't already a tenant of that building?
Or, this example that I've walked by a few times: I can't remember exactly which building it is (somewhere on 2nd Street maybe), but it's a relatively tall office building whose footprint is something like this:
The black area is the building, and the white area is glass-enclosed and looks like a lobby or food court... but really it's just a big empty space filled with tables. It goes all the way up: there are no building-floors above it. There are no storefronts or vendors inside. It's incredibly uninviting, and always empty. And next to the street-facing glass doors is a plaque that says something like "DESIGNATED PUBLIC SPACE, OPEN 8AM-9PM." They could have just left the glass off and planted some trees, but instead someone thought this walled-in concrete slab was a better idea.
purple_b tells a story of how, years ago, one of the local papers published a list of these so-called "public" spaces downtown, and he went and visited many of them. But he no longer has the list, and my google-fu fails me on searching for anything like that.
I would like to find such a list.
I'm also curious about what the actual zoning rules are that result in this kind of thing.