That was a different era
LOL, tell that to Kobe Bryant and Jermaine O'Neal and Marcus Camby and Shareef Abdur-Rahim and Allen Iverson and Stephon Marbury and Jeff Fucking McInnis. Duncan would hav ebeen picked ahead of all of those early entries.
https://www.infoplease.com/sports/1995-1996-season/underclassmen-nba-draft