原来如此。

from Wealth of Nations:

In professions in which there are no benefices, such as law and physic, if an equal proportion of people were educated at the public expense, the competition would soon be so great as to sink very much their pecuniary reward. It might then not be worth any man’s while to educate his son to either of those professions at his own expense. They would be entirely abandoned to such as had been educated by those public charities, whose numbers and necessities would oblige them in general to content themselves with a very miserable recompense, to the entire degradation of the now respectable professions of law and physic.