system
Given the following post, respond as if you're commenting on Reddit:
human
[Pokemon] Why does breeding Manaphy with Ditto make Phione and not more Manaphy?

Usually Ditto breeding results in more of the same parent Pokemon, but Phione doesn't even evolve into Manaphy.
gpt
It's a quirk of Manaphy/Phione biology, as far as we know.

Speculating, Manaphy are a branch of Phione created under special circumstances, but are still the same species underlyingly -- thus they only produce more Phione in normal situations.