Since these guys were li'l snot-suckers they've been told that they 'can do anything' and that they 'deserve a shot'. Apparently the NBA execs did little to break them of their spoiled habits. They are used to getting what they want and not having to deal with consequence. So when they DON'T get what they want, they pitch the fit.
The NBA isn't the only sport, either. I propose eligibility based on performance, grades, record and community involvement. We'd then have responsible, civil, conscientious players. We'd also then have only 30 players, though.
Unfortunately, what you say is true. Several years ago, the Texas Legislature considered enacting a law that stated that individuals could not enter colleges as athletes unless they were otherwise eligible to be students at the institution. In other words, they had to be academically eligible to go to a college before they could play sports for the college. A bunch of Texas college coaches went down to Austin and had a fit. They stated that there would never be another national championship in any sport in Texas if they enacted the law. The bill was killed.