I once knew a traffic-light engineer who was an EE with a BS. I mentioned that I thought it was annoying not to have sensors on lights in rarely-used cross streets, since it wastes a lot of gas to have the main throughway traffic constantly stopping for no reason, not to mention wasting people's time. He said that if you put in a sensor, people will get used to the light always being green, and in the rare case it turns red they will tend not to stop and will cause more accidents. He was very strongly opposed to such sensors - arguing supposedly from experience as a professional and an expert - and our argument started to become, well, heated, so I just let it go. I really doubt what he said is supported by statistics, but his attitude was an example of the thinking of the people designing the lights.
(This was a couple of decades ago. Maybe the thinking has changed since I do see more sensors these days, but still not nearly enough. Often they seem poorly designed, such as unnecessarily waiting a full cycle before changing even if there is no cross traffic.)