Too much pressure; too little coping skills.
Kids thrive in middle school where the teachers are told over and over, "Never do anything that might make a student feel uncomfortable or embarrassed" and are allowed to retake quizzes until they get the grade they want (if your school doesn't, it's coming...). As a result, almost all kids earn all As and Bs.
Kids thrive in high school where teachers are put on an improvement plan if 80% of students do not earn 80% or higher. Zero tolerance in some schools means that comments that make the student feel bad are not tolerated even if it would have been considered "positive peer pressure" in the past.
Even our local community college has switched to the "multiple retakes are available if the grade earned wasn't the grade desired" plan.
Freshmen often struggle in college. Are we surprised? For many of them, it's the first time they've made any major decisions by themselves - and for some, mom/dad is still choosing the college or the major. Many are sharing a room, choosing when to get up, whether to go to class, and when to do homework for the first time in their lives. We have seen so many kids, especially excellent high school student athletes, that either didn't go to college or moved back home after a year.
When kids graduate, but can't get a job and have student loans to pay, it has be overwhelming. We, as a society, haven't taught them coping skills for life's little disappointments, so why are we surprised that they don't know how to handle the big issues?