It is fundamentally less efficient to run electrolysis on water to produce hydrogen, and then reverse the process again in a fuel cell to produce electricity to turn a motor, vs taking the electricity used for that electrolysis and storing it in a battery that is then taken back out to turn a motor. Granted, modern lithium battery chemistry isn’t the cleanest thing to extract and use, but it’s also not the only possible battery chemistry, just the one currently most used for vehicle batteries. It also doesn’t allow for certain benefits to BEV like home charging (I mean technically one could run a hydrogen line to one’s house, but that doesn’t seem likely). The only scenario I can think of for hydrogen cars taking off is if the needed infrastructure was built out for something else and so was readily available. I could maybe see that if hydrogen ends up getting used as the solution for decarbonized aviation fuel, but my understanding was that it (along with basically every other proposed tech for that admittedly) had some pretty serious cost drawbacks and so there’s no garuntee of it getting built out for even that application.