Exactly this, they don't use the same API. It would be a pretty big effort to get Kbin working on Jerboa, it's likely that mobile apps specific to that will pop up soonish.
API support in KBin is currently on the roadmap but disabled (for now). Hopefully once there's a working API for KBin, an app will materialize. I have my suspicions that there still won't be interop (you can use a Lemmy app for KBin or a KBin app for Lemmy) for a long time, but I definitely think it will make KBin instances a more attractive link aggregation community solution
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