With the new CBA, it makes all the sense in the world to come out early if you are gonna be a 3rd or higher round pick. Maybe even lower than that.
Before, the top picks got tons of money, so it made sense to stay if you thought you could shoot up from the 2nd or 3rd to the 1st or even from late 1st to high 1st. But now that the top picks aren't getting ridiculous money, that particular pot of gold isn't there. Additionally, the CBA makes it so players can't get extensions or new deals until after their third deal. So before if you were a 2nd or 3rd round pick and you blew up, you could hold out and renegotiate right away and get your payday. Now, that door is closed as well. So the only way to really get paid, is to get to free agency. The earlier you get to the league, the earlier you get to free agency.
The new CBA definitely takes away a lot of the incentive for 2nd-4th round type college kids to decide to stick around another year.