It has only gotten worse since the 60's because now YOU and I can afford to fly. Back in the "golden age" people flew maybe once a year and saved in order to do so. Even then it was mostly well to do people flying - now it may as well be the bus. The relative price per ticket now compared to the 60's is nickles.
I flew on spirit airlines a few months ago round trip from DCA to DFW for $128. That's INSANE low. In 1960 dollars that would have been ~$16. You weren't flying anywhere for $16 in the 1960s.
People wanted to fly, so the airlines accommodated that by smashing us together and giving us low fares - making themselves not really that rich in the process.