That's a great question. It's that way because I always make the access to controls more ergonomic. We switched the entire assembly to left side here due to toilet. But if this was a walk in shower I would have left the slider bar/shower head on wet wall and just relocated the valve. That way you can turn on shower without getting wet. Here is our typical set up.

This makes perfect sense to me! Makes me wonder why more showers and tubs aren't set up this way.

Where are the drains in both pictures? Thank you!

One more question.... why do you put the control only (not the entire assembly) on the opposite wall for a walk in shower ? Thank you!

I prefer the shower head next to the toilet out of the way of the entrance. Also seems better to lay in tub with your head away from toilet. I prefer the control valve on the back wall allowing you to turn on shower without getting wet as well as operate valve while standing under shower.