Well, they did allow the direct hs to NBA in the not so distant past (LeBron’s group) and the NBA must have decided there was a good reason to instate the ‘one year out of high school’ rule. I think it was because the NBA wanted their recruits bigger and more experienced and while a few players may be ready to play right out of high school, most guys are still growing and are better players for the college experience.
My kids went to school with a baseball player who had to choose between college and an MLB contract. In the end he chose college. He had good advising as his father is a top sports agent. Baseball has its own farm/training system so it doesn’t really need the collegiate system, but uses both the minor league system and the college system to develop players…
For many sports, the kids are giving up real money to stay in college - golf, swimming, tennis, and basketball. The Olympic swimmers give up millions to swim in college but they feel it is worth it. The low amateur at the Masters looked sooo excited to be sitting next to Tiger, and he had his college shirt on. He could be making some money on the tour but he’s staying with school for now. A few basketball players are one-and-done, but most stay longer.