An academic environment provides not only
disciplined study and
rigorous evaluation, but a
safe environment in which to do so. The dirt-under-the-nails of market experience can be acquired in a summer's internship.
Want proof?
Size up the income of a trader with a bachelors and 4 years of experience, against a Masters (CFRM, etc) and two years of experience. In 10 years, see who's supervising whom.
The reason these programs exist is that the market deems them worthwhile through salary.
"Price signaling" as the economists say....