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If you don't think of evolution as a part of every Pokemon's life cycle, as in a Nidoking isn't an adult Nidoran it's just a Nidoran that evolved into a Nidoking, it's not that weird. Like I'd imagine the species as a whole consists almost entirely of Nidorans that can breed, with a small number that grow powerful enough to evolve into Nidorinos/Nidorinas with the latter losing their ability to breed in the process. Naturally occuring Nidokings or Nidoqueens are probably incredibly rare considering they have to be willfully exposed to a radioactive rock. It's not like the species only survives because Nidokings are using Nidorans as fleshlights every night.
Also canonically the reason why Nidorina and Nidoqueen can't breed is because they have to give up their ability to breed to stay as powerful as Nidorinos and Nidokings. That lore predates the games actually having a breeding mechanic and it's reflected in game despite never being referenced.
