Kerosene is about the most energy-dense chemical fuel we have, and long-distance flying is... impractical, without it. What alternative do you imagine to the jet engine?
Hydrogen is markedly more energy-dense than kerosene, by unit weight. It takes up more room, and in particular more room than fits in wings. So it needs a different tankage scheme. Underwing nacelles seem practical.
Hydrogen works fine in jet engines, but also in fuel cells driving electric turbines.
Once aircraft using hydrogen enter a route, kerosene craft become unable to compete, because the huge reduction in fuel weight translates to substantially increased paying-cargo capacity.
It will depend on infrastructural changes, in particular synthesis from grid power and storage at airports, and a cheap renewable-power surplus.
It's to create an alternative engine technology.