In those days, before Chrysler Motors, Southwest Airlines and Amtrak, a person could very easily be born, live and die all within a radius of 50 miles. Aside from the county sheriff, the only authority-figure the average man ever knew was his parish priest. Priests had to wear many hats. They were lawmen, judges, family counselors, little league coaches, doctors, psychologists, teachers, supervisors of church administration and building maintenance, and on top of all this they were required to write letters and sermons, to hear confessions, and to perform rituals. Nobody in his right mind would envy the lot of a l4th century parish priest.
Mystics are spiritual anarchists.
You can't tell someone who has a direct-communication link to God what you think the divine word means or the divine will intends. A mystic can figure that out for himself. He prefers to tell you. The last thing a priest needed was a few mystics in his congregation challenging his authority. He had enough to do without having to coddle these troublesome elitists.