Here's why:
* Different technology: Rock Band microphones use a proprietary wireless technology that is not compatible with the standard USB microphones used by Disney Sing It.
* Different connection types: Rock Band microphones connect wirelessly via a receiver that plugs into the Wii console, while Disney Sing It uses USB microphones that plug directly into the Wii console.
Therefore, you will need to use USB microphones to play Disney Sing It on the Wii.