That's because they use high-pressure tanks.

Actually higher working presure than regular welders' oxygen tanks.

Too bad the higher the pressure, the heavier the tank, especially steel.

I had a pretty good job offer from a company that was going to start building CNG tanks out of carbon fiber.

This was a few years before the failure of the Titan submersible.

CNG has made some progress since then, here's the kind of thing there is now:

https://steelheadcomposites.com/sites/default/files/2024-01/...

COPVs are not exactly a new tech. They're just taking a while to proliferate to those lower end applications.

Not like it's a necessary thing. CNG conversions were already viable even with 00s steel tanks.