Earlier quoted context omitted.
I still don't know why radar does not detect aircraft on a collision course. Why technology still does not track every airplane at the airport and flag runway incursions. Why there still are not cameras constantly recording flight ops at the airport. Why are we relying on accidental dash cam recordings? Why the cockpit voice recorder still does not record video.
Radar sweeps, it takes time to get back, it takes time to relay information and it takes time to respond. When you have aircraft moving at hundreds of miles an hour crossing in close proximity the trajectory can change and result in impact before radar can gather data, assess it, make a prediction and relay that information.
All well within what we can do with radar and computers and radio today.