Any particular reason why this runs outside the cluster?

Main reason is that I wanted to be able to support single VPS K3s clusters all the way down to ~512MB.

K3s already takes up about 100MB which only leaves 400 for the application, so trying to run Canine on that machine would probably create too much bloat.

Don't know anything about this project, but usually the reason is "because there could be N clusters", and sometimes "because I want the cluster to come and go frequently" (e.g. for testing workloads).