Why does it matter how long the Dream Team played in college? That was a different era.
If I have to explain it to you then you have already missed the point.
Here is a short/simple explanation though:
When you look at that team, there will never be another team like that assembled. Take look at how many of those players were/are either elite and/or HOF'ers.
The NBA began to crumble after the olympic team in 2000. When the high schoolers and unproven foreign players began to dominate the draft, this started earlier, but around that time. There wern't too many stars taken when this began. You have more exceptions rather than rules. The last few years as the players have started to attend college have made the game better, the talent is deeper as they have developed or not.
Think about a player like Savlik Randolph, who would have been a high pick out of high school, but goes to Duke, is not worth they hype, still leaves anyway and is a nobody and I don't remember if he was even drafted.
It just makes sense to see these kids, again kids, against real competition not high school kids to get a better feel for who they are. Again, not all players are Kobe/LeBron/Garnett as they are on a whole different level to begin with.
Say what you want, but the erosion of the NBA coinceded with losing in the Olympics, high schoolers and foreign players dominating the draft. When people talk about how the rest of the world caught up with the USA, it is a farce. The USA fooled everyone by thinking the NBA was the deepest and most elite league in the world. It simply was not the case, but it is beginnig to change again and will do more if kids go to college for longer periods of time, or don't enter the NBA and become lottery picks when they clearly aren't ready or proven.