They may have inbound and outbound routes at busy GA airports in the USA but I bet they don't have them at the same altitude like here.
if you have a CTR up to A015 with CTA above (big jets!) with outbound routes at A010 and inbound routes at A015, what other inbound levels can you have?
In those days there was no International student flying schools so traffic was much less
maybe (?) at PF and JT, not BK, AF and MB.
Remember few ATC's have pilots licences so looking at it from a pilots point of view didn't enter the equasion
A large number (particularly back then) of GAAP ATC hold/held pilots licences - that's what attracted them to GAAP in the first place.