First, because hydrogen is small, it leaks. It will seep right through most containers directly, and something like a screw on cap.... fuggedaboudit.
Second, because its light, it floats, You can't keep the stuff in a bucket. Open the tank. All gone.
Third, the very thing that makes it useful as a fuel, is how damned flammable it is. You really don't want to be sitting on a cannister of hydrogen gas if it catches on fire... makes gasoline seem pretty tame. firecracker vs earth shattering kaboom.
Here's where metallic storage comes in... a few years back someone discovered metallic hydrides work pretty well. Imagine a honeycomb of foamy metal formed into a block. Under pressure you can force the hydrogen to seep INTO the metal, and by forcing it, it doesn't have enough energy to seep back out... unless you heat it up. Now you got a big rock that's got a lot of hydrogen in it, Not gonna explode on you.... not gonna leak. not floating away. I saw a demo once where someone used a chainsaw to cut a block of this fully hydrogen charged stuff in half... No earth shattering kaboom He then put both pieces back in the car, and could use it again.
But you gotta heat it up to use it. and that makes it a problem. who wants a car you have to wait twenty minutes for it to warm up before you can pull out of the driveway? Yes yes, I know old people who do. They had them, once upon a time, and don't mind so much. I do not though... it's a step backward.
And THAT is where the breakthrough here comes in. You Don't have to heat it up so much. You can get in the car with one of THESE chunks replacing the gas tank, and using a hydrogen engine drive right away.
This is a big deal.