>>40588412The Nidoqueen line are extremely competitive when it comes to breeding.
The younger Nidorans didn't get a chance to breed at all because the bigger, stronger Nidorinas hogged all the dick to themselves, leading to a stagnant gene pool.
Nidorans who became infertile Nidorinas ironically had a better chance of their progeny surviving and breeding, leading to the Nido structure we see today, with Nidorans breeding and Nidorinas protecting.
Nidoqueens are rare in the wild because a Nidorina would need to find a moonstone, but the same applies to them.
