Manhattan is extremely construction-friendly. There are, however, limits. It's already an extremely developed city, so there's no real empty space left. Any construction will involve buying out existing owners/tenants, demolition, and replacement.
This is happening, but naturally is not fast. There are reasons why you wouldn't someone to demolish a skyscraper in the middle of Manhattan without oversight.
Adding to this problem is the state of infrastructure. Manhattan streets are packed, and most subway lines also. There is currently a proposal to up-zone the area directly around Grand Central and raise the height limits. This is a great thing, except all subway lines feeding Grand Central are already operating past peak capacity. Creating this extra space is pointless (and in fact detrimental) unless there is infrastructure ready to support it.
There are already infrastructure projects in place to alleviate this, but digging tunnels through bedrock is understandably not a fast affair. The East Side Access project will connect Penn Station and Grand Central, and alleviate some of the traffic at both. Adding to the complexity here is that Manhattan's underground is already filled with tunnels of all varieties, forcing new projects to tunnel ever deeper, with requisite cost and slowness.
The world is complicated, city planning is complicated. This isn't software where we can just deploy a new server - apartments, offices, subway lines, streets, sewers, power plants, cannot be willed into existence at a whim.
Do you live here? Because there are lots of empty lots and there are tons of under-developed areas. I don't know why you believe "Manhattan is extremely construction-friendly"; it's certainly not 'construction-friendly' enough so that there are numerous affordable housing options. Some crazy number of housing units are under either rent control or rent stabilization. The housing dynamic here is insane.
I do live here. I know of exactly one substantial empty lot in Manhattan - just south of the UN building. I still wonder what the plan is there.
Hell, the biggest development project going on right now involves building on top of a train yard. This does not suggest an availability of actual empty land.
> "and there are tons of under-developed areas"
And yes, that's precisely what I referring to when I mentioned that any new development would have to involve demolition and replacement. Replacing a 15-story apartment complex with a 45-story apartment complex may be a good idea, but first you'd have to buy out all the owners in the building.
That sort of thing is neither simple nor fast.
The infrastructure problem exists still also. Spanish Harlem can be argued to be underdeveloped - and we can surely replace those buildings with tall apartment complexes... except the 4/5/6 subway is already massively oversubscribed. You can build apartments there, but said residents won't be able to get to work. The 2nd Ave Subway is supposed to alleviate a lot of this pressure, but we all know how fast that is going.
Same goes for basically all of Upper Manhattan - there are plenty of opportunities to replace buildings, but not enough infrastructure to move people around. Transportation (like most cities) is the biggest developmental bottleneck.
> " it's certainly not 'construction-friendly' enough so that there are numerous affordable housing options."
You've missed the entire point of my post. "Construction friendliness" is not Manhattan's bottleneck. Lack of infrastructure, and systemic slowness inherent in building replacement (read: buying out existing stakeholders) are. For all intents and purposes, Manhattan is "friendly enough".
There is a building that's finally going up near me in the Lower East Side - a replacement of an old walkup. The owners in the old building resisted sale for a long time, as it would involve displacing them, plus they (rightly) speculated that their property value would continue to increase. The solution at the end of the day is to offer existing owners a brand new (albeit small) apartment in the new building. Not only did it cost the builders money to demolish and erect the new building, but also to buy out the old owners and give them part of the new property for free. Things like this are why Manhattan is replacing buildings so slowly, not because Manhattan is somehow opposed to development.
Please, visit Istanbul sometime. It follows those rules pretty closely. But don't just visit the historical districts -- visit the neighborhoods where there's a random skyscraper in the middle of otherwise low-rise residential. Nearly everyone gave up on building attractive buildings.
There is a character to a city, and it is easy to destroy the things that make them worth living in.
Manhattan could re-zone to permit a great deal more construction, but it is unlikely to happen.
First, residents strongly oppose it.
Second, much of the transport system is maxed out. Building more housing or office space would only overburden systems operating at capacity. (e.g. the west side highway, fdr drive, lexington avenue subway line are all unusably crowded)
What is the zoning like in Manhattan? I see intermingled residential/office/commercial spaces everywhere I go (heck, my last office was in the same building as apartments, with a store-turned-restaurant on the ground floor), so I didn't realize there were zoning restrictions in that sense.
there are crippling height restrictions all over the place, and you have to buy un-used "air rights" from your neighbors to build anything taller than what already exists in the neighborhood
environmental impact studies (weirdly) can be used against projects
local "community boards" have a lot of power
and the aforementioned centrally imposed limits on development -- the city's top-level boards may not like what you're doing to transportation
Or if new construction is impossible, they could also encourage companies and residents to relocate somewhere else, thus reducing the congestion burdens on those who remain.
But what city with taxing authority would ever do this? As long as cities can take revenue from everyone regardless of their satisfaction with the city, there is a perverse incentive to oversubscribe city services. Since they are a monopoly over their whole territory, it is the same pressure as upon telecoms to add more customers without building out infrastructure.
