Hydrogen is much less expensive than helium, gives slightly better lifting performance, and is not a scarce resource. Why don't more HAB projects use hydrogen?

Hydrogen is much less expensive than helium, gives slightly better lifting performance, and is not a scarce resource. Why don't more HAB projects use hydrogen? The only good reason I can think of, discounting the fire hazard, is the poor reputation of high pressure hydrogen tanks for the reverse Joule-Thomson effect (i.e., unlike most gasses, hydrogen heats up when expanded out of a nozzle), but according to [1] it is not enough to cause ignition. [1] Health and Safety Executive. 'Spontaneous Ignition of Hydrogen'. Research Report RR615, 2008. URL: www.hse.gov.uk/research/rrpdf/rr615.pdf