I guess the answer is obvious:
There's not enough space for a 2nd touchpad on the left side. And even if there were, one of the two touchpads would have always been useless.

That being said, I get your point. Maybe it would have been clever to have a modular design in that part, which allows you to swap the touchpad and the number keys around.
This however would have required to split the keyboard and would have made also the internal design more complicated. Also one would need at least a 3rd module for the mouse buttons.
The easier approach to address left-handers would have been a trackpoint instead of a touchpad.

The button in the middle right below the display hinge is a fan switch, so you can decide whether you want the device to run passively or not. I think that's the best option, because in other situations you'd want a fan to dissipate the heat and increase the computing power.

Besides, If you place a dark laptop in the blazing sun, so it really heats up, you won't be able to touch it with your bare hands long before the plastic melts. Plastic may deform before that point though (X220/230 anyone?).
That's why I generally think, bright colors (white, silver, light gray) are more reasonable.