Weight is definitely the most important issue for a plane, but at some point volume also becomes a limiting factor. Yes, you can stretch an airplane, but that also makes it heavier. With jet fuel, they're currently using every available space, storing most of it in the wings and some also in the fuselage. That's much harder to do with hydrogen, because the pressure containers can't just take on any shape. They have to withstand absolutely insane pressures, so they have to be either cylindrical or spherical.