1 - renewable surpluses. As wind and solar keep ramping , hydrogen is a fantastic way to store that energy. Sure, there are efficiency losses but it's transportable, able to be stored long term, and able to be used from small scale to grid scale applications

Grid storage is a genuine problem that needs solving, but there's no particular reason to believe hydrogen is going to be the technology to fill that niche. There are much simpler and more efficient competitors, not least of which being pumped hydroelectricity, but also including exotic technologies like molten salt thermal plants or compressed air mineshafts. And batteries, for that matter; once portability stops being a concern, other battery chemistries start to be an option which don't include lithium at all, like sodium-sulfur.

And even if hydrogen electrolysis does make sense as a grid storage medium, there's no particular reason to think it's a good idea to package up this hydrogen, transport it, and stick it in vehicles to convert into electricity through their own mini power plants. The alternative, where hydrogen is simply stored and converted back into grid electricity on site to meet demand leveling requirements seems far more likely.