Based on third-hand versions of events I've heard, it's a mixture of bureaucy (no one was ever fired for ranking Nature on top), (inter)national rankings ("I know this conference is better, but those are the rankings the funding agency sent us") and the amount of people willing to champion an issue in a board meeting. And then there's inertia: "This ranking got us good researchers so far so I see no good reason for changing it and devaluate everybody's publications".

I've never witnessed straight corruption, but I did witness marketing teams sent to prey on researcher's fears. So I wouldn't discount that too.

Informative and concise. How can I subscribe to both of your journals?

In the social sciences, higher-ranked journals publish higher-impact (that is, more highly cited) papers. This is not causal but those journals tend to publish palpably better motivated, better explained, and better executed studies.

When you go up for tenure, your publications are still fresh, so your impact is hard to know. So the rough rank of the journals in which you publish is a proxy for it. This is why universities reward publishing in some journals rather than in others.

Why do higher-ranked journals publish better studies? This may be for a number of reasons. Better studies are more likely to be submitted to higher-ranked journals first rather than to lower-ranked journals. Researchers who write better referee reports are more likely to accept requests to referee papers at those journals. And the editors may shepherd papers at such journals better too.

Notably, predatory journals do none of these. It is no surprise that publishing in predatory journals will not get you tenure nor promotion at such universities.