It's preferential treatment of their own. It's maintaining and staying in control of their proverbial kingdom by any means, and making sure their children are in line to inherit the same benefits.
Every civilization and Kingdom or whatever you want to call it that is at the top of the social caste does this. Particularly if they're the ones who established said kingdom.
If wakanda existed they're not about to let a bunch of cacs come in and gradually overthrow the rulership thier people have established. Either you're on top or you're at the bottom.
The answer to the question is more nuanced than just one pillar/aspect of their overall control. It's everything.