Mainly because of a little thing called aerodynamics. An object shaped like an enormous wall is harder to move through the air than one that’s a little more streamlined. This is why most of our aircraft (whether lighter- or heavier-than-air) do not resemble vertical walls.
But as Dan Grossman from Airships.net points out, media outfits like CNN and the Daily Telegraph have been completely fished in by a clever PR stunt that has zero chance of being built in the real world.
What began as a fun exercise by a London design firm — to illustrate the visionary creative abilities of the firm and its client, Samsung — has been picked up as if it were a real “news story” by CNN, the Telegraph, and other media outlets.
The firm of Seymourpowell, which has previously designed vibrating sex toys and packaging for tampon applicators and cat food (but has never engineered an aircraft) recently announced “plans” for a 100-passenger, octahedron-shaped, 870-foot tall luxury airship, inflated with over 11 million cubic feet of… flammable hydrogen. (Yes, just like the Hindenburg.)
— Grossman, Dan. “Hydrogen Airship Nonsense.” Airships.net, 3 February 2010.
Well, the basic shape would still make a pretty cool cat food bag; though I doubt that it would be any good as a tampon applicator.