The girl ducks never want it, and are continuously evolving newer vaginal canals with more turns and bends to prevent the ducks from fucking them .
The males keep evolving newer, more nefarious dicks to get them with.
Reminder: all duck sex is rape
Wait what
How do the females evolve more labyrinthine vaginas? How would something that reduces likelihood of reproduction get passed down?
Cause most duck procreation isn't consensual. The males would rape their species out of existence if it wasn't for the females that survive passing on more labyrinthine vaginal canals that block the male duck penis from killing them.
So it's to prevent physical damage from the rocket cock, not to prevent sex.