What happened to Giant Flying Boats?
The rapid development of aircraft in the 1920’s and 1930’s far outpaced the development of aviation infrastructure to support them. Runways, even by the late 1930’s, were rare and often little more than an open grass field, useful only for the smallest and lightest of airplanes. It would be at least another decade until many cities developed suitable airports. But commercial aviation wasn’t going to wait around.