I'm not an expert, but it has something to do with rooting invalidating DRM keys. It was circumvented for the Z3C: https://blog.al4.co.nz/2015/01/good-news-for

I'm not an expert, but it has something to do with rooting invalidating DRM keys. It was circumvented for the Z3C: https://blog.al4.co.nz/2015/01/good-news-for-z3-compact-owners/ https://blog.al4.co.nz/2015/01/good-news-for-z3-compact-owne... But it seems like it was a very deliberate choice by Sony.