As others have pointed out it might be used for flight/boats.

In general though saying it isn’t useful for cars is kind of missing the point of new sources of energy. New sources of energy (and the associated prime movers) allow new forms of transportation.

For example you couldn’t really make a car using steam power. That was only possible with gasoline and an IC engine.

Looking at it another way: what new forms of transportation would be possible with hydrogen? Personal flight maybe?

We do a lot of really inefficient things if there is a market for it.