It's all about how a player projects to the next level. There are plenty of guys who were backups or low level starters at smaller schools that were more impactful than say, a Tyler Hansbrough from UNC. The guy was one of the most accomplished players ever in the ACC and he is out of the league now because his skill sets just don't translate to the NBA and he's not athletic enough. There are plenty of guys that went on to better careers you probably didn't hear of at that time in college. Skal Labissiere was another one who didn't play much at all in college but goes on to be drafted in the first round.
Much of this is just how scouts project a player at the next level and finding a fit with a team. Some may need to go develop their game in Europe or the D league but there are plenty of guys who didn't dominate in college who become good pros.