Many traffic lights do react to traffic to adjust the timings. Look at the road surface, the thin black tarmac boxes, diagonals are electronic field sensors that can detect if a car is over them. Great for vehicles to trigger a light change, but useless if your on a pushbike
All the sensors will do is speed up a change if there is nobody going from a certain direction. The lights will have a maximum setting they will stay green on a direction, in part to stop traffic congestion elsewhere.