If you’re going to have one and dones, set up the draft like MLB. You get drafted out of HS or after your third or fourth year of college. If a player gets drafted but doesn’t sign an NBA, NBA D-League contract, or sign with an agent, he can go to college and play.
Also, make scholarships four years. Once you give a player a scholarship, it’s good for four years and is non-transferable. Leave after one year or flunk out because your majoring in basketball, the scholarship is dead for the last three years. Allow transfers if the coach leaves or is fired with no scholarship penalty. See how many schools jump on the one and done bandwagon then.