Because you know you want to.
We had a situation here recently where my wife had to give up her Lumia to our youngest son and pull an old Android out of her bedside table drawer and use that temporarily. Our whole family used to be Android users, but they all followed my lead and switched to Windows Phone about a year or so ago. It's been a while since my wife has used an Android device and it wasn't long at all before she started complaining about it. She has a new Windows Phone on the way and can't wait until it gets here. She mentioned that the experience difference between Android and Windows Phone is like the difference between a garage sale and a real store. Android may have the apps, but Windows Phone is just a better, more intuitive experience. If only more people could experience that.
One of the biggest drawbacks for a platform switch like this has been the ability to transfer personal data. Fortunately, Microsoft has just released an app for both Android and Windows Phone that helps ease the transition.
Named "Switch to Windows Phone," the app transfers contacts, text message, photos, videos, and music between Android and Windows Phone devices. It does this one of two ways:
Move data over Wi-Fi – creates a virtual wireless connection between the devices
Move data over OneDrive – moves data from Android to OneDrive and then pulls the data down once the Windows Phone is configured and app installed
Windows Phone version: Switch to Window Phone
Android version: Switch to Windows Phone