So WHY exactly is Xbox music on WP such a mess?

I mean what is the technical reason?

I find the difference in performance between the old music app and xbox music mindblowing. I keep running into people saying that it's not native. They mean it in every sense (not written in native code, de-coupled from the OS.. Are these two connceted on WP?).

I'm just wondering if there is a person here with the knowledge and the insight to clarify this.