Cause it has a touchpad like a laptop.
I don't get it either. Who ever plays games on a laptop using the trackpad? It sucks for games and it sucks for browsing. It just sucks for everything, but it's the best option for a laptop. With game controllers though, there are much better options.
If I was making this, I'd put the touchpad on the upper right. Dpad on the upper left, and two sticks on the bottom. Basically playstation except right buttons replaced with touchpad. That'd give it so much more flexibility, ala a best of both worlds approach. Really really don't see why a touchpad on the left makes sense. Computer games use wasd. That's even less precise than playing with a d'pad.
Except there's no touchpad O_O. Unless the second analogue stick replacement counts as one. in which case, is worse than using the touch pad on the Dual Shock 4