Their sex act also has to happen in a half-second, because the lymph that inflates that giant curly fry can't hold it taut for more than a second. Oh and, of course, female ducks have vaginas that corkscrew the OTHER WAY, so only the fittest males with the biggest and most maneuverable penises can jam them in there in the few moments they have for their lymph to do its thing. And all duck sex is a surprise to the lady duck, so guy ducks have to be expert at sneaking up, rapidly inflating, jabbing, and then presumably swimming off quickly before the surprised lady duck beats the shit out of them.
Do other waterfowl procreate this way? No, of course not. Can you imagine a swan with a giant curly dick? Ducks are just the total freaks of the natural sex kingdom. A duck sees you reading Fifty Shades of Grey and tweets "LOL humans smh,", right before ripping a massive curly boner. Don't even try to out-freak a duck.
Info source: Yale Scientific Magazine