The fantastic thing about mobile, specifically Android, is that it's all one platform. There are no proprietary game cards or one specific device that you must
have to play the games. Some games, such as Need for Speed: Most Wanted, even feature cross-platform multiplayer with iOS. If you've ever seen China's game tablet factories, they have Android systems of all shapes and sizes.
Maybe you want a 7" or higher screen for a true tablet experience, or a small screen so that you can carry it in your pocket (or something like the Vita and Galaxy Note have, in between). Compared to the 3DS which only has two models or the PS Vita which only has the standard 5" model, there is an Android device for everyone.
Most mobile devices also feature HDMI out, basically giving users a "console" experience at home. Perhaps if handhelds were designed more like this, they would be a more enticing purchase.