1 it would require building out entirely new infrastructure, running up against severe NIMBYism at this point. It's incredibly hard to even build new power lines right now. Try a highly combustible, very leaky gas.
2 it's far cheaper to just strip H2 from natural gas, which releases carbon (unless you capture it, increasing cost), so not carbon free unless you force using electrolysis from renewable power sources
3 Electrolysis efficiency is ~70%, fuel cell efficiency is ~60%, so round trip efficiency is <50%. Much more waste than a battery (~80%). You're both using essentially the same electricity to create the power, but hydrogen is wasting more of it, so will necessarily be more expensive
4 in vehicles, fuel cells end up charging the battery toi power the motor anyway, so the energy loss from the battery is a wash
The one thing they have is range and speed to refuel, but as batteries get cheaper and better that will be minimized before H2 gets big enough to take over.
There's lots of big companies with smart people who are still pushing for this so hopefully they know what they are doing (mostly in Japan it seems)