Greninja not available in either Generation VIII Pokémon mainstream video games??? Why?

As of Pokémon Day 2020, Greninja was named Pokémon of the Year 2020, because he has received a total of votes from most of his fans, making him the #1 most popular Pokémon of all time overall worldwide. But unfortunately for most of his fans, it was so disappointing that Greninja, along with his Ash-Greninja bond phenomenon, was not made available in either Generation VIII Pokémon mainstream video games, even though he was playable in Pokémon UNITE and recruitable in Pokémon Café Remix (née Pokémon Café Mix), but without his Ash-Greninja Bond Phenomenon. So I wonder why you think? Please let me know, thanks.