Why can't I just play my media (which I paid for) on my hardware (which I paid for) in "normal" software (which... I thought I paid for). Instead I have to have the Xbox brand shoved in my face at every opportunity?
I know this isn't your point, but you might be happy to learn that Xbox Music and Xbox Video have been renamed in Windows 10 to "Groove Music" and "Video", respectively. According to Microsoft, most users thought "I don't have an Xbox, why would I want to use Xbox Music?" — so they rebranded those apps.
WMP was never a great player, but at least it would ship the necessary DVD-reading machinery as well as a license for using it legally.