This is an intriguing new wrinkle. "So there's more than one world with Pokemon. Takato-kun and I are in a similar situation."

Except in Takato-kun's world, the Digimon at least cosmetically looked similar enough for there to be a card game, apparently. (Ken has a Wormmon card in his back pocket as he speaks.) Why would that be different....?

The idea of "why wouldn't it" is too big to wrap his head around.