Hydrogen takes up more cargo or passenger space. That sounds like a real problem when that’s cutting into an airlines already very tight profits. But here’s the thing. Fuel cells require vastly less servicing than combustion engines! So overall the CASM (Cost for Available Seat Mile) goes down! That means, although there’s less seats – the savings on the cost per seat is actually so low the airline might make MORE MONEY per passenger.
Less passengers: but more profit per passenger! In smaller flights anyway. Larger flights have other challenges – but they might burn the hydrogen in an engine.