Those wings are expensive

Growing feathers requires substantial amounts of proteins with scarce amino acids.

Cranes usually take 3 years to replace all their primary flight feathers. Only albatross have a more extended molt schedule.

Unlike ducks and geese, cranes do not become completely flightless when they molt their wings.

Note the slotting of the outer primaries to reduce turbulence at the end of the wing – same as upturned wingtips on jets.