[walrus01]

Helium is rare and expensive and becoming even more so as time goes on.

Hydrogen has this nasty habit of being extremely flammable.

Rigid or semi-rigid airships when scaled up are really difficult to moor and arrange ground handling for, which is why some of the recent prototypes that have been flown integrate skirts and reverse-hovercraft like suction apparatus that can hold them down on a flat field.

The empire state building was originally intended as a Zeppelin mooring location, but the plan was abandoned due to wind and inability to control a zeppelin to that level of precision.