Local files

[user-removed]

There are a few threads on this but they are all quite old. From Spotify's own Guide:

It's currently not possible to download local files for offline listening with Windows Phone.

What I want to know is... why? What is the limitation? What stops them doing this? I have had a Premium account for quite a while but since switching to WP and finding myself having to switch between different music apps to listen to all my music, I may have to reconsider and go with MS's own offering.