Why do most tenure at an institution less prestigious than the one where they began teaching, and than where they received their Ph.D?
This is called the &quot;law of descending prestige.&quot;

Most universities hire the most prestigious faculty they can.
The number of PhDs from the top universities is larger than the number of job openings at universities.
Therefore, so long as PhDs seek employment at universities, most of them will get jobs at less prestigious universities than their PhD university.

It is not &quot;inexorable,&quot; just probable.