My dude, the military transports more volatile materials than hydrogen every day. Just because something doesn't make sense for civilian use doesn't mean it's never going to be viable for military use.
If you're worried about the dangers of transporting something like hydrogen, you're going to lose it when you find out what bombs are made out of.
Electric motors are just more efficient in just about every way at scale, the current diesel motors being used in tanks aren't really able to be improved upon. They're at their technological peak, so the only way to move forward with mbt is by figuring out how to make electric motors work.
Why? If something has gotten through the armour, your fuel is the least of your worries. I mean you are sitting next to a stack of shells filled with high explosives.