From Little League through high school, our sons climb the ladder in incremental steps. Those who are offered the opportunity to play in college suddenly find themselves in the midst of the top 10%-or-so of all high school players; and many on the college roster already have from 1-3 years of experience playing at that level. Throw in the need to perform acceptably in the classroom and the time away from home, and the magnitude of the challenge increases appreciably.
What had been progress up measured rungs becomes a leap of several rungs' distance. No wonder that it doesn't work out for all who attempt it.