It's not an adaptation of the show. It's based off Digimon World for PS1. Digimon pooping was apart of it. I forget exactly what it did but I think it had to do with their happiness and virus levels, contributing to the branching evolutions. Portable Potties are convenient so the player doesn't...
I've been lurking here since March and I made an account just to say that this should be the official reply to all that ask. It's not like those people have been reading beforehand.