ADS-B as it is called now was turned down by both the FAA and the DOD when I suggested this system of aircraft tracking in 1989. I was a radar, communication (sea, land, and satellite) and navigation tech that liked to fly search and rescue for the CAP and realized using the GPS how accurate this type system of aircraft tracking was over the ATC radar I maintained.
The problem has always been the fear of a single point of break down, jammed GPS signal. It is a handy side safety system that has no real back up. They are warming up to it now with numerous ground stations that can augment the satellites.
It still isn’t quite there yet, but once the ground stems are in place that can be ‘boosted’ they will likely move to it.