Didn't we cover all this recently?
Realistically, most of the students at umpire school realize after the first three days that the odds of them getting a job in pro ball are pretty slim (did you ever notice that "slim chance" and "fat chance" mean the same thing?). That's why we lost 35 guys the first week - they gave up and went home. The rest wanted to become better umpires - and MAYBE get a shot at pro ball - so they endured.
I did not get a job in pro ball, but I'm glad I endured.
JJ
PS A few guys (older, retired, or not yet tied down to life in the real world) were sent by their local associations to learn as much as they could and then conduct clinics back home.