Kris needs it for... something, and the SOUL needs them to be able to do anything BUT move around. Makes sense they put us in the birdcage, given how much we.... WANDER in ch4. Just a silly headcanon i got

[ Arrow pointing to Kris: Annoyed having to keep it kennelled and in the dark about their schemes. ]
[ Heart shaped arrow pointing to SOUL: Clueless, poorly trained service animal type thing. ]