With more and more teams drafting players right out of high school and many of them seemed to be a wasted pick after a few years. In 2005, the NBA decided that the 2005 draft is the last that players under 19 or within 1 year out of high school are allowed to be drafted.
Tom Heinsohn on BDSSP said: ”when he was playing there were 80 players in total, now a days there are 150 starting players...Back then players were sign with teams knowing that they could play and now players are sign based on their potential.”
LeBron was a special case on how successful he was right out of high school. KG, LeBron and Dwight Howard were the only three who played significant minutes in their rookie season. LeBron’s and Howard’s physical strength were just amazing when they were 18, but the rest of the high shoolers do not have a NBA body like these 2 had.
Most of the players that come out of high school, teams are banking on their potential only, look at Kobe, T-Mac and J O'Neal they all had limited minutes and didn't show their talents until 2nd and maybe later years. Then there are Kwame Brown Tyson Chandler and Eddy Curry, who still have yet to live up to their hype and many more who are even worst then these three. Even Greg Oden right now, watching the NCAA tournaments, the analyzers said his offence is still raw and need a couple of years to develop when he goes to the NBA but without the age limit, Oden would had been1st pick last year or even the year before when he was 17.
The problem of picking players based on their potential is that most of them do not develop in time and get traded or sign with another team before they become a good player, not to mention those who don't develop, therefore most of them are a wasted pick.
T-Mac, J O'Neal, JR Smith, Telfair, Curry, Chandler were wasted picks, Rashad Lewis(I think he is leaving the Super Sonics this year and he) as well. Robert Swift had not done anything yet, the Celtics had Jefferson, Green and Perkins and only Jefferson is playing well. None of these players had a good rookie year. And did you see what happened to Shawn Livingston?
Why do teams draft them?
Most of these players were not ready yet but NBA teams were willing to pick them hoping for a big paid off in the future. Because they still make money when their team do not make the playoff next year and get another high draft pick, they don't want to see a potentially good player go to another team.
So if you look at the NBA as a whole, one year in college is a good decision, since almost all the prospects out of high school are players who have potentials only, they are not necessarily better player then those who are drafted behind them at the time. NBA teams are only picking these players because if they don’t, someone else will. Therefore, the age minimum is good for the league as a whole but not necessarily good for any individual team. The NBA is just forcing teams to pick the more NBA ready players.