I think the focus on shooting came from USA getting their ass beat in international ball for a few years in a row in part due to a large number of the best players not being the best of players. That lead to the NBA changing the rules to try and encourage more three point shooting and player movement and to take some of the physicality out of the game. Combine that with the Seven Seconds or Less Suns success adn more teams starting trying to copy that formula as they saw the benefit of having shooting to spread the floor out.
I mentioned earlier on here that the emphasis on shooting threes came as the league reduced certain rules like illegal defense. There was a time that no more than 3 players could be above the 3 point line. One of the first teams I saw do this (have 4 players outside the 3 line) on a consistent basis was the Barkley sun's and the 93 - 94 rockets.
The zone defense which forces teams to pass more, 5 second count which hurts posting up, lack of fouls called when posting up and fouls called more on penetration and when players are in the triple threat has put a more emphasis on shooting. But it makes since if you eliminate posting up the only options left are driving and shooting.
Then you had teams like the 91 Lakers and those isiah championship pistons who had their PF become stretch 4s to give the guards room in the paint. Since both teams did not have dominant big men.
Actually if you go back to those pistons teams they were the first teams to win multiple titles with without a dominant big man. They were also one of the first teams to roll their PF (laimbeer at center at times and use him as a stretch 5 to shoot 3s). The pistons killed teams with speed, depth, versitial big men and length.
We look at them for their physical play on defense but actually on offense they were similar to teams of today.