>>962256They were around because transatlantic voyages typically couldn't be done in a single shot, and airports were still in their infancy, meaning stopover locations typically had no landing strips
They went away with the advent of bigger airports and long distance airliners capable of making a transatlantic flight in a single shot. That, and they're not particularly good at being a plane or a boat.
They are still useful in firefighting and SAR roles, though, and they are cool looking
