Why traffic signals don’t talk to each other?

One evening, I was walking on the footpath in Chennai. Followed behind me the sound of an approaching ambulance, alarming me about its urgency. Unfortunately the signal turned red. How long will the ambulance be stuck here, I wondered. Strangely, the motorists ahead of the ambulance decided to drive, despite of the red light. To my surprise; motorist around the other signals (even if they were green) froze! I found this interesting that even though the signals were not intelligent enough to detect an approaching ambulance and ensure that it passes through first, the crowd did.

I wondered, why traffic signals don’t talk to each other, why they are not intelligent?