Also, as you point out, this is a very-low-paying field. Someone who isn't from a wealthy family will struggle to live on the kind of pay they will get, meaning

Also, as you point out, this is a very-low-paying field. Someone who isn't from a wealthy family will struggle to live on the kind of pay they will get, meaning that they are more likely to work in the field for a few years, then get married, have kids - and need a real income. And now the next hiree has to go to all the trouble of re-establishing relationships with donors. I just read a reasonably interesting book (In the Garden of Beasts) about an academic who became FDR's ambassador to Nazi Germany. One of the points that the author repeatedly makes is that such positions were very much the preserve of the wealthy, who were expected to spend substantially from their own pockets for both official and unofficial events. Living on his salary alone was an unusual and unpopular move, even within the State Department.