“Do they really need to include every Pokémon in the next game?”

Look, there are a lot of logistical reasons for why Game Freak stopped making every Pokémon available in each game during Sword and Shield. There’s also a lot of very valid criticism that removing Pokémon from mainline games feels directly at odds with a series that is all about attachment between player and pocket monster. But this argument has been going on for four years and Game Freak seems intent on standing its ground on this issue. So just spare yourself the headache of digging that grave.