I can see why
Why buy NSMBU if you can get NSMB2?
Why buy Tropical Freeze when you can get Returns 3D?
Why buy 3D World when you can buy 3D land?
Why buy Rayman Legends when you can get Origins?
Because one is a game you play on a tiny screen with a significantly less powerful system, and another is something you play with a controller and an HD system on your couch with a huge TV?