I have no inside GM information, but I’m sure it all had to do with production cost, and the perception that customers wouldn’t care what the step side fenders looked like. GM had done a great job designing the 55 rear fenders and if there was a perception new fenders would increase sales, there probably would have been a fresh design to compliment the 1960 cab.
But back in 1960 very few people bought these trucks for personal enjoyment. Since the overall truck styling was a complete departure from the previous series, it appears the entire styling budget was focused on the fleetside model. I read an article recently that claimed the 1955 rear fenders were originally intended to continue in production for the new 1967 series. A disapproving designer, without executive approval, created the new design we’re all familiar with now. Management saw the concept and ordered it into production. If this hadn’t happened, they may have continued using the old design throughout the 70’s. And this thinking is not without precedent. Consider that Ford stuck with the same stepside fender for 26 years and several cab designs from 1953-1979.
Personally I thought the 1960 step sides looked stupid when I first saw them. I was only 12 at the time, but was a car nut all my life and style was important. At the time I actually thought the factory must have run out of the new parts and just put old fenders on until the new version became available. Over the years I’ve grown to like the way they look, but still think they would have looked better had they at least widened the fenders and steps a couple of inches to line up with the sides of the cab, like they finally did on the 1973 models.
