They did not have to take a picture of that many travelers in the 90s (let alone social media which did not exist) and it wasn't less secure either. They probably never considered if their program is any useful or if it creates more harm than good.
Although until 9/11 the intent usually was either to get to a non extradition country, or demand something from some nation state primarily.
The source above shows a clear decrease in airline fatalities through the years but I suspect that’s due more safety improvements through autopilots, better sensors, and more redundancy than the decrease in hijackings.
This is nothing to justify the massive surveillance.