MS used to own the mobile platform (along with Symbian). After iPhone first released, MS took too long to respond and let the iOS and Android took over the market. After seeing the success of Apple, MS attempted (IMO) to copy Apple's business model including arrogant attitude of Apple. It turned out to be a major failure. Windows RT or WP may be the better devices (on its own), but the ecosystem still cannot compare to iOS or Android. The market is already saturated, unless MS can do something revolutionary, there won't be any chance for Windows RT or WP to succeed.
The only chance for MS is to expand x86 platform to mobile and stops being arrogant like Apple.