Why are fields susceptible to critical theory and postmodernism also characterized by low income and low intellectual rigor?

Just an observation. The other day, in When data verifies impressions, I mentioned that along with Studies, Anthropology, English:

Other sources seem to indicate a prevalence of postmodernism and critical theory among the psychology, sociology, communication and education departments as well.

Quite separately from that conversation, I was checking anticipated incomes by university major (here is one source and a second and a third).
I noticed that those degrees that are most prone to postmodernism and critical theory are also those with the lowest employment prospects (except for the education department) and the lowest starting and career average incomes.

It is not particularly surprising but it does prompt a question of causation and directionality.

Low income degrees tend to be clustered around very human relation fields which also tends to be fields with little objectively determined domains of knowledge. If you are going to be an electrical engineer there is a very broad and deep domain of empirically established knowledge which is invariate from New York to Nicaragua to Nigeria to the Netherlands to North Korea. It is a field that is both in demand and requiring high levels of knowledge acquisition to a very precise degree. None of which is true for, say, Sociology which has only a small domain of invariant knowledge and which is taught dramatically differently by country and culture.

So is the prevalence of discredited critical theory and postmodernism in the lower Humanities fields a consequence of some historical path dependency or is it perhaps because those fields require less intellectual rigor and therefore are more receptive to CT and PM, or is it that people in those fields are angry and envious of their low income valuation and therefore more receptive theories such as CT and PM which deflect responsibility for outcomes from personal agency to systemic explanations?

I don't know but it is striking to see the clear correlation between receptiveness to CT and PM and low income and low cognitive rigor.