Because the controller by design does not need a dpad. It only needs extra buttons in case you run out of practical mapping.
You have a left analog zone and haptic feedback on it. And a right analog zone with haptic feedback. Each zone notices the difference between push down and just swiping on the surface. Each zone also has 3 parts, where you can do stuff like map things to the outer and inner edges.
So for a lot of 3D games, you would do something like
-Left analog is left zone. Outer edge is used as dpad(since dpad is only used for rare commands.)
-Right analog is mapped to right zone, but so is the face buttons. Swipe = Move camera, push down = use button. Outer circle is still not used for anything, but can be.
-Map bumpers and analogs to the back, just like on the original gamepad setup
-Start/menu is start/menu, and select/back is select/back.
For 2D games, you already got a nice primary surface. Just map the "dpad" to the left touch surface, and use push down. And face buttons to the right surface. Its not magic.
Its not hard to map the controller to work for a game like Starcraft either, since you can do left zone for panning and right for mouse control. You also have 8 buttons free for control groups.