We have vast tracts of gaffa criss-crossed by fixed routes that are inefficient for airlines to fly. Works for ATC without surveillance and low traffic levels.
Increase the traffic levels and introduce non-fixed routes (flex tracks and UPRs) and it comes to a point where it no longer works for ATC without surveillance. At least not without increasing controller numbers considerably. Solution, introduce surveillance.
Dick, when was the last time you saw how ATC is done?