1. It is a different game.
2. Not all players continue to improve; some peak early.
3. Considering how many players end up as full busts, and both hibbert and green have had relatively long careers, its not like they are complete zeroes.
4. College playoffs are 1 and done, so maybe they got lucky and were overrated.
5. As already pointed out, there are lots of college teams and the maximum career is 4 years so college talent is waaay more dilute than the nba, so any team with 2 or more actual nba quality players is going to be good, even if neither are stars.
6. Both were juniors in 06-07 which is a huge advantage compared to freshman, but is actually quite shown to make you a WORSE long term nba prospect because you are closer to your peak, with less room to grow, and youve already developed in the college world, which has less intense training than nba. So they were likely overrated at that time as nba prospects since they were playing against freshman and sophomores but had less nba upside.
7.Just as with talent, size is more diluted in college, so becomes less of an advantage in the nba.