Probably because of how the roads were designed. It's symmetrical, yes, but the traffic flow go in opposite directions.

On the left side where there is a traffic light currently, it's all well and good because the line where the cars have to stop is right before the street gets all curvy.

On the side that goes north, you're driving along a curve that goes right. If there was a red light right there where OP drew the imaginary crossing, the cars would have to line up behind each other in a curved fashion. When was the last time you saw traffic light placement like that? There's a good reason why there isn't: that kind of light placement makes it much harder to see pedestrians because other stopped cars in other lanes would block your view of them.

If you don't believe me, open up Google Maps streetview, go put the camera in the center lane where the you imagine you would stop your car for pedestrians, then imagine a slowed or stopped car to your left there that was blocking your view. If someone were to cross from the left to the right just then, you would not see them and would hit them.

Contrary to popular belief, stoplights in bad places INCREASE casualty rates.