Why do you think Nidorina and Nidoqueen cannot be bred?

Yeah, what the above said. It was merely a glitch that they overlooked when they created the breeding mechanic in Gen 2, but they've since kept it for some strange reason. Considering it makes zero sense to leave it untouched is rather questionable, as they've had six following generations to fix it but left that problem intact. In short, it was at first glitch that they kept for whatever reason they had.

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