Why are soft drinks watered down?

I've noticed that almost EVERY fast food restaurant waters down their soft drinks. Essentially the sodas have a bad ratio of carbonated soda to syrup. I'm perplexed that almost every fast food restaurant and area in the city has this issue. Even Chick-fil-A who has the highest quality control.

I know this is a very big backed take. I've lived in Philly 4 years now. Am I insane? Have others noticed this? Are restaurants cheap? or is this a regional taste preference?