Riolu can be found in the wild in Unova after only being a rare event mon in DPP, or from the HGSS safari. Likewise, Zoroark can be found wild in Kalos following their rarity in Unova.
How would you feel about old starters receiving the same treatment? In future regions they become rare wild encounters. Would this be an acceptable excuse/change for not including every starter? If Bulbasaur/Squirtle/Torchic etc were obtainable in the wild in Alola, for example, or Charmander/Chespin/Froakie etc being "native" to Galar?