The dream of “order a flying taxi on your phone and it takes you wherever you want in five minutes” isn’t really compatible with aviation safety culture (at least at the pilot level in the US). That’s not to say it can’t be done, but you probably need a lot of really good PR people to figure out how to say “we want to remove the safety controls from this so we can make money with it” and have people buy it.

Maaaaybe instead of the tunnels and bridges, to increase throughput during rush hours, but even then we’re trying to have fewer vehicles in Manhattan, not more.

Also, I cannot imagine what it would be like to go through an intersection during the winter. You would be hit with a wall of cross-cutting wind tunneling down 50 blocks that no airborne device is going to handle well. Absolute nightmare.

* Any failure tends to turn flying things into unguided missiles

* Noise is extremely hard to control -- I did an FAA helicopter discovery lesson, and oof

* Cities tend to have difficult to manage wind currents and hit-or-miss visibility. I was in a skyscraper across from one hit by a helicopter trying and failing to land in 2019 -- there's reasons for city no-fly zones

* Limited landing sites makes them highly situational in the first place, unless you want your streets to be helipads, which you don't

These are all fairly intrinsic and not mitigable. I can think of more issues more in the sticks, but you get the idea.