I dunno.... maybe its because guys were not afraid to customize back then ?Finish the ride ,drive it for a few months and then customize the headlights and tail lights or do larger body mods like chop the roof ,therefore giving the impression that they were never done which leads to everyone believing they were in primer ......if its not finished ,it must be in primer type logic ...... I dunno
It does seem that alot of people have the wrong perception about what was or was not ,back then.
Like I have said before I do not exactly when there talkin ,but I have hotrod mags all the way back to the early sixties that show finished rides,say that some of the pics were readers rides,not big time car builders and listed many many articles on painting your hotrod like a bass boat with lots of metal flake,not metallic like todays paint ,more like giant snow flakes of glitter