So many hippies with long hair.. not many haircuts! Did Barbers hate the long hair whenever they seen it, and want to cut it all? Cause that's what they live off of... Or did they love that time, so they didn't have to cut as much hair?
There were plenty of people back then who didn't grow their hair out, especially during disco. Not just the crew-cut rednecks either. And anyone who wanted to sport "Jesus Hair" (like Andy Gibb) were in the stylist's chair 3 times a month, so longer hair was not a hinderance to the barbering business. When the HIV look became popular in the 80s and 90s, the barbers saw a surge in business. It's like any fashion I guess.