The NBA is not going to give big enough contracts to prospects just to send them to minor leagues. Players can play in other countries for way more than NBA minimum contracts or paltry NBDL contracts.
Baseball can have a minor leagues because is it not a popular sport internationally.
I guess having a real minor league system would could work. We would have to re-allow drafting out of high school, and allow teams to have 25 man rosters, with only 15 in the 'big leagues' at a time, and rules for optioning players back and forth. This would also remove pressure to play draft picks right away.
I do not think the Players Union would ever agree to this, since the salaries for the minor league players would make less money available for the veterans.