Batteries are too heavy for aviation. Hydrogen flammability can be mitigated due its tendency to escape very quickly into the atmosphere (lots of tests on ruptured tanks floating around).

Hydrogen can also produced as a form of storage when the grid is producing more than it consumes which is not uncommon with renewables. Yes batteries are denser and more efficient but they are expensive and lithium is still a problematic resource to mine. Water electrolysis is cheap and easy to deploy.

It's a decent stop-gap solution for low emissions until battery technology becomes dense enough for aviation.