In plenty of countries this is a reality already. Sensors are placed anywhere from a few meters to hundreds of meters ahead of the actual lights to determine the flow of traffic, there are 'green waves' which you can synchronize with to guarantee uninterrupted passage (both for congestion control and to save fuel) and there are adjustments made based on the expected flow from different routes depending on the time of day.
The future, in this sense at least, has already arrived.
Sure there are plenty of places where this is not common yet, but infrastructure upgrades are expensive.
It's a bit more involved than that, nowadays there are many sensors instead of just one to detect a waiting car in front of the light, the speed gets measured as well as the number of vehicles.
As for a 'simple' camera, nothing that you deploy in all weather conditions is ever simple if it is to operate reliably.
The future, in this sense at least, has already arrived.
Sure there are plenty of places where this is not common yet, but infrastructure upgrades are expensive.