Fifty years ago, American Airlines' flight from New York to Los Angeles took 5 hours and 43 minutes. The same flight is 6 hours and 27 minutes today. Wendover Productions examines why planes don't fly faster in this interesting video.
A lot of it is the significant increase in air travel. The bulk of air travel in 1967 was business travel, because flights were still fairly expensive. The rest comes down to engineering, as explained in the video.