https://www.si.com/nba/2015/09/11/john-calipari-nba-hall-fame-ceremony-former-players
Even in the article you posted, Orton, Goodwin, and Teague still got first round guaranteed money. Nothing is 100%. Not everyone is gonna make it. Cal's point is that you go when you can get the money, and those guys did and got more than well compensated.
But even when you consider the handful of kids in that article, Cal was joined by 64 former players, most of whom are very successful pros. They love him because he has their interest first, which is why he pushes them to go pro when they can get 1st round money.
Likewise, he'll tell the ones that aren't for sure 1st round that they should consider coming back if they can improve their stock.