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Game Freak has no one to blame but themselves. It's not like Nintendo expecting a new Pokemon game is a new concept. The pattern is pretty established.
Tired of working on Pokemon, but don't want to give up the IP? Hire more people and create a division that is only for Pokemon. Then have the original company work on whatever new project they want to do. Either you'll make a popular new IP and still get money from Pokemon or it'll fail but you'll still get money from Pokemon. It's win/win.
Keeping the company so small while essentially being in charge of one of the most popular franchises in the world is on Game Freak. Nintendo didn't demand that Game Freak never grow in size.