My guess is that it is about political will. If people in career services want a fief where "Guarding their gatekeeping function was of greater concern than doing their job." -- then it will take political capital to fight that. Depending on their incentives, university bosses might not bother.

But the Ivy League schools know that their bread is buttered by their ability to get students into elite positions, so they make sure their career services department gets things right. And have been doing so for so long that these departments do things right on their own.