Why are some "compatible parents" slots empty?

Question

This has happened a few times now, I saw an egg move I wanted on one of my Pokemon (ex. Salazzle with Fake Out), I clicked on the egg move and the only compatible parents that're shown are the Pokemons pre-evolutions/itself. This also happened when I saw Oricorio could learn Quiver Dance through breeding, but the only other Pokemon with that move were Oricorio? I know this most likely isn't a site error since I tried checking another site for the same egg moves, and they were also blank.

Comments

For Salandit, I think you'd have to breed it in an older game where it has compatible parents, like Kangaskhan or Scraggy, and then transfer to SV when it becomes compatible with Home.

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These are likely the mirror herb exclusive egg moves. The site does make this a little confusing though.