Why do some people say that the Airline Deregulation Act of 1978 lowered ticket prices by a lot when the rate of falling prices were already happening prior to the passage of the law?

From Brookings:

“Every serious study of airline deregulation in the intervening years has found that travelers have indeed benefited enormously. As we documented in our 1995 Brookings book, The Evolution of the Airline Industry, airfares, adjusted for inflation, fell 33 percent between 1976—just before the CAB instigated regulatory reforms—and 1993. Deregulation was directly responsible for at least 60 percent of the decline—responsible, that is, for a 20 percent drop in fares. And travelers have benefited not only from low fares, but from better service, particularly increased flight frequency.”

https://www.brookings.edu/articles/the-fare-skies-air-transportation-and-middle-america/#:~:text=Deregulation%20was%20directly%20responsible%20for,service%2C%20particularly%20increased%20flight%20frequency.