Because KBin had more features than just what's available with federation because it's a separate codebase than Lemmy. I'm starting to get it now, thanks for the help!
KBin federates with Lemmy nicely. Meaning you can, while logged in to a Lemmy instance, subscribe to a KBin magazine. However, you cannot log in to a KBin instance directly
Right. As of now there's no app that allows the full KBin experience on android. I'd expect it to come in the future, but first KBin needs some API work