What part of them is not sustainable when over 95% of the battery components can be recycled right back into new cells with zero loss of functionality? That means at a certain point almost no new materials will be needed. I'm curious what you mean by not sustainable.
Indeed they are but there are so many problems with hydrogen it is DOA in my opinion. Who wants to be tied to a fuel pump? I'm so happy to have ditched the need to stop at a fueling station every week it's not even funny. To be able to 'fuel' at home (or literally anywhere there is an electric plug) is a huge benefit to EV ownership.
Plus it isn't hard to find all kinds of problems with hydrogen. For one it's hard to contain without it escaping. But the largest issue is that you're using electricity to create hydrogen that is stored, transported, stored, pumped to cars, then used to create electricity. You see the problem there right? Using electricity to power an EV means that 75% of the power is directly converted to the wheels. Where as hydrogen is less than 25%. It is far less efficient to use - and it's not even close. Much better to just use that initial energy to fill a battery.
And hydrogen costs are about double the cost of gas - $0.25 per mile vs $0.14 for gas or $0.03 for an EV charged at home. That means over 100,000 miles of ownership a hydrogen fuel cell vehicle will cost you $14,000 more than a gas car or a whopping $22,000 more in fuel than an EV. That's another compact car! Cost is a huge deterrent for consumers. Perhaps eventually the infrastructure improvements will help bring this cost down - if it survives long enough.
That said, I believe there is a place for both. Hydrogen may be a good fit for mass transit. Bus, train, semi, etc. But I don't see it ever catching on for the general commuter car.