Microsoft is already using the Unity3D engine on Windows Phone

Many developers complain that Windows Phone, at the programming level, there are several limitations and constraints such as the ability to use graphics accelerators to create cross-platform games.

Dan Ardelean, developer, has announced via Twitter that Microsoft used safely in the game engine Unity3D Kinectanimals since it needs a lot of resources that XNA can not satisfy. The question then naturally arises, whylimit the developers to use this type of game engines? If you already have access to these developments it seems strange that has not yet been released.