Hydrogen is actually less dangerous than batteries

Tell that to the Hindenburg.

When there is a leak, it generally dissipates fairly quickly and fires or similar are quite rare

It's more the risk of hydrogen embrittlement, which can cause sudden catastrophic failure of their containers.

And, broadly speaking, it's not an issue because hydrogen cells aren't commonly in use for retail civilian consumption.

As soon as you've got a bunch of big tanks zipping around on bumpy tracks at high speeds...