Because the draft is so susceptible to a bad pick and 1 good player can dominate an entire team. One bad pick and you're screwed. The NBA has the fewest team members of any major professional sport so the individual is more important.
Case in point are the Detroit Pistons who had the #2 pick with that young stud Darko Milicic. They'd be the NBA champs if they had gone with DWade instead.
The Spurs got Tim Duncan and that setup the franchise for a decade.
Portland picked Sam Bowie instead of #23. Everybody knows how that went for both franchises.
In 2006, the Bobcats blew their wad on Adam Morrison instead of Rudy Gay. So they still suck.
2005, Milwaukee picked up the super Andrew Bogut. Atlanta who desperately needed a point guard decided to get a shooting guard in Marvin Williams. Meanwhile, the Jazz picked up leftover Deron Williams and the Hornets picked up that Chris Paul guy. Atlanta would be a top 10 team right now if they had just picked up a point guard they knew they desperately needed.
2004, went pretty much OK, except the Lakers picked up Vujacic at #27. Half the guys before Sasha aren't even in the NBA anymore.
Kobe Bean Bryant was a #13 pick that the Lakers only got on a draft day deal for Vlade to the Hornets. Why didn't the 12 teams before choose him? If the Hawks had Kobe, they'd be dominating the league right now. The Lakers would be a loser team without that lucky #13 pick.
The Pacers are a worst case scenario, they're always good enough to make the Playoffs but not good enough to win it all. So they never end up with good lottery picks. Let's see what they do with theirs this year.
Stupid-ass draft picks make for bad parity.... The NBA, where one man happens.