What do you think about the Davis-Moore hypothesis? Why are some people with very important functions in society (such as producing food) paid so little if the hypothesis is accurate?

In 1945, Kingsley Davis and Wilbert Moore published a paper outlining what they believed to be a credible hypothesis about the causes of social stratification. Davis and Moore believed that social stratification was functional in nature; in other words, they posited that society is complex, each group in a society relies on the others, and perhaps most importantly, society is self-regulating. In this worldview, they actually suggest that economic inequality is necessary because it fulfills an important societal function. It is overly simplistic to argue that the Davis-Moore hypothesis says a job's importance to society will always lead to higher pay for the person who does the job. Instead, they posit that the more scarce a particular vocational skill set is, the more remuneration the worker should/would receive. In response to your question about food producers receiving lower pay, Davis and Moore would likely argue that food production must not be a particularly difficult responsibility, and that would explain why its workers would not be paid at a premium. Davis and Moore actually argue that if a certain job (let's use your example, food production) is necessary to societal functioning, it should continue for the good of society and accept its status for the good of the group, even if the people doing the job aren't paid well. The accuracy of their argument is often debated more than sixty years later, and many consider the Davis-Moore theory flawed and circular in nature because it never explained why issues of pay continue to exist in industries that many argue are very important and require specialized skill sets. Their argument about social stratification also ignored the ways that wealth is amassed in the upper classes through inheritance, investments, and other factors.
http://faculty.upj.pitt.edu/dsantoro/davis_moore.htm