There are lots of cities with very urban airports - London, Toronto, San Diego, Pheonix, Boston, Mexico City, Rotterdam, Washington DC... and for a lot of those, it's their primary airport not a secondary field. I really don't think it's a fair characterization, and for a lot of those cities it's viewed as a huge benefit to have easy access to an airport from the downtown. There is a reason London City has grown as it has over the years and why even airports like Chicago Midway or Ronald Reagan in Washington can be so successful - proximity.