Ditto and Egg Groups

[Greninjaman]

I got a question about this little guy: On Bulbapedia's page about Egg Groups, Ditto has its own designated Egg Group. If it can breed with anything that is also able to breed, would it not make more sense for it to be included in every Egg Group (other than the undiscovered/No Egg Found Group) as opposed to having its own dedicated group?

 

[Arceusgjengen]

No, because it can't breed with itself, and it can breed with gender unknown Pokémon, while other gender unknown Pokémon can only breed with Ditto, if they are not in the No Eggs Discovered group. If Ditto was a part of all groups, why can't it breed with itself?