I think in university the issue becomes largely one of limited time and effort budget. I was an engineering major and took some economics courses for a minor (which I never got in the end) that involved essay writing. The issue wasn't that I didnt know i could improve it by editing, it's that each piece of homework competes against each other piece of homework for time and attention. The goal is 'how good can I make it in the time I can justify putting towards it'.
I'm sure I made some boneheaded errors in some of my work but I was already doing 'homework triage' and leaving the least valuable but time consuming assignments to when I might be able to get to them.
Writing a work you intend to publish rather than submit to a teacher is a different exercise. It's hard to practice in an environment where you're already racing the clock to get your 4-6 hours of homework out of the way each night.