Second, because the hydrogen for a flight will cost less than kerosene, because it was made on-site rather than pumped, refined, and trucked in. Further, it was made at the time of day when grid power was cheapest.
The result is that an LH2 operator can always undercut a kerosene operator, anytime they compete. The kerosene operator only gets flights the LH2 operator passes up. Thus, the LH2 operator also gets the most profitable routes, because those are where they choose to bid.
Even after synthetic kerosene becomes available, it will necessarily cost more than hydrogen, and not anyway be made on-site, and still weigh too much.
I'm told this has really big impacts for aircraft design, which will put hydrogen aircraft at a big disadvantage compared to kerosene fueled vehicles. I could be wrong on this, and don't have any references handy, so I definitely welcome being corrected on this.
In particular, increasing volume by a factor x means growing the skin by only x^1.5. Tankage is only a small fraction of aircraft volume. So, even though space in the wings, where fuel is put today, would go unused, the amount of extra weight for new tankage would be minimal.
If, as I expect, tankage is slung under the wing alongside the engines, airframe design would not need to change, and existing aircraft could even be retrofitted. Lifting bodies are supposed to be more efficient and have lots more room inboard, but efficiency might get less important as fuel cost plummets.
Ultimately we expect aircraft to move to electric-driven turbines, attached to fuel cells. Tankage and fuel cells could be anywhere convenient on board. It seems like there would be safety reasons to keep the tanks outboard, as the kerosene is, mostly, today.
Anyplace where LH2 aircraft are in use, kerosene craft will be found to be completely unable to compete.
Thus, starting on key routes, kerosene craft will be driven off to less profitable routes. Demand for LH2 craft will be driven by need to stay in the market at all. The earlier adopters will profit most, initially pocketing the huge difference between current prices and their own cost, and later by wholly owning the most profitable routes.