Bill Starr has this to say:

"The standard of strength from the time I first got interested in physical culture up until the early ’70s was the overhead press."

...

"Then several things happened that changed things dramatically. First, there was the emergence of the sport of powerliftlng. Competitive weightlifters who were having difficulty mastering the quick lifts found that they could utilize their strength much more readily by doing less dynamic lifts: bench press, deadlift and back squat. Nearly every pioneer in powerlifting was a former Olympic lifter. Except for a few rare exceptions, these athletes stopped doing overhead presses completely and spent more time improving their benches. The next event that influenced strength training’s shift away from the overhead press to the flat bench came in 1972, when the International Olympic Committee dropped the press from official competition. Finally, this is when strength training for athletes really began to grow. High schools and colleges across the country soon had strength programs, usually run by an assistant football coach. Because the overhead press had gotten some bad press when it was eliminated from Olympic competition (it was supposedly a high-risk exercise for the lower back) coaches opted to go with the much safer flat bench.

For the record, it was never proven that overhead presses were, in fact, risky to the lower back. The real reason the Olympic Committee dropped the lift was because the judging had gotten completely out of control. The press became a political tool, and instead of cleaning up the officiating, they took the easy way out. In a few short years, the standard of strength shifted from the overhead press to the bench press."

Source: http://library.crossfit.com/free/pdf/CFJ_Bench_Starr.pdf