Nursing school is a lot of bookwork. How to prioritize, critical thinking, and of course how to pass the NCLEX. You don't spend a lot of time actually doing the work. Inserting catheters, IVs, NG tubes. Not on live people anyway. My hands on course was at the beginning of my schooling before clinicals. Makes sense right? You need to know how to do these things before clinicals. Thing is I never did a single one of those things during clinicals. We were on Med surge units and many of those things just don't happen that often. We were specifically prohibited from inserting IVs (a huge thing where I work ER) because of liability issues. I know several students that did urinary catheters but I never did.
Even our days on the unit we were expected to gather enough information on our patients to write detailed care plans
and you had to hand write most of the information since you couldn't print it due to HIPPA. That's a lot of clinical time where you are not delivering hands on patient care.
Last reason is that nursing school is general information. A unit is very rarely general. There are burn units, neurological, orthopedic, pediatric, maternity, OR, ER, psych, etc. You don't have enough time in school to learn each in detail. That's why there's always a learning curve even with experienced nurse when switching specialties.