[dandotway]

Hydrogen Embrittlement[1] is not discussed in the link, an effect where hydrogen diffuses into metals and causes them to become brittle and crack. Many aerospace materials are especially vulnerable: high strength steels, nickel and titanium alloys, etc. Fueling a disposable balloon or rocket with hydrogen is one thing, but a vehicle that can safely be refilled with hydrogen over and over for decades is quite another. (Recall how the rust red Space Shuttle External Tank was not recycled like the white SRBs were and was the only large expendable component each launch.)

[1] https://en.wikipedia.org/wiki/Hydrogen_embrittlement