because helium is f'ing expensive an valuable. Once used, it's basically gone. There's a reason that countries have strategic helium reserves.

Also on the topic, modern day companies that try to resurrect airships exist. Just every single one of them goes bust, as it's just not really a viable solution for modern transport

You may know this, but the Nazis were forced into using hydrogen instead of helium because the only commercial sources at the time were in he USA and we wouldn't sell it to them. But also, since the ship was built for German propaganda they would have wanted it to be a fully German endeavor.

The Hindenburg was painted with silvery powdered aluminium, to better show off the giant Nazi swastikas on the tail section. When it flew over cities, the on-board loudspeakers broadcast Nazi propaganda announcements, and the crew dropped thousands of small Nazi flags for the school children below. This is not surprising, because the Nazi Minister of Propaganda funded the Hindenburg.

At that time, the US government controlled the only significant supplies of helium (a non-flammable lifting gas), and refused to supply it to the Nazi government. So the Hindenburg had to use flammable hydrogen.

As the Hindenburg came in to Lakehurst on May 6, 1937, there was a storm brewing, and so there was much static electricity in the air - which charged up the aircraft. When the crew dropped the mooring ropes down to the ground, the static electricity was earthed, which set off sparks on the Hindenburg.

The Hindenburg was covered with cotton fabric, that had to be waterproof. So it had been swabbed with cellulose acetate (which happened to be very inflammable) that was then covered with aluminium powder (which is used as rocket fuel to propel the Space Shuttle into orbit). Indeed, the aluminium powder was in tiny flakes, which made them very susceptible to sparking. It was inevitable that a charged atmosphere would ignite the flammable skin.

In all of this, the hydrogen was innocent. In the terrible disaster, the Hindenburg burnt with a red flame. But hydrogen burns with an almost invisible bluish flame. In the Hindenburg disaster, as soon as the hydrogen bladders were opened by the flames, the hydrogen inside would have escaped up and away from the burning airship - and it would not have not contributed to the ensuing fire. The hydrogen was totally innocent. In fact, in 1935, a helium-filled airship with an acetate-aluminium skin burned near Point Sur in California with equal ferocity. The Hindenberg disaster was not caused by the hydrogen.

The lesson is obvious - the next time you build an airship, don't paint the inflammable acetate skin with aluminium rocket fuel.

https://www.abc.net.au/science/articles/2004/02/26/1052864.htm

To add on the point of helium being expensive and valuable, it's also extremely important for supercooling MRI's and supercomputers.

I'd rather have more MRI's than zeppelins.

Look at the Akron and Macon. Big advanced helium filled. Zeppelins don't handle weather well.

Helium is twice as heavy as Hydrogen, much harder to find on earth (it's literally named Helium because until recently it was believed to only exist on the Sun)

So more expensive and you gotta use a lot more of it for the same lifting power, also Hydrogen can be used for this safely, the Nazis just were cutting corners to not have to give any credit to the Americans who at the time had a monopoly on the resources that would have let them go with helium or that would have let them coat the ship safely.