The 3 point shot changed the game...the full court press is risky unless it's executed flawlessly, it leaves too many wide open 3 point shots.
I loved to watch teams that pressed, Maryland was one of the last teams to use it somewhat effectively...Duke will use it from time to time still.
My answer - the 3 point shot and too many good ball handling big men, back then you didn't have big men who could run and catch the ball like they can now...Therefore, it is easier to break the press and punish the team that is pressing you.