Many of them are fairly gifted writers who enjoy the process. Many others hate to write and do it very poorly. Becoming a better writer takes time. Progress is incremental. Repetition is essential.
Epiphanies are few.
All writers, especially struggling writers, need full and thorough feedback. As a newspaper editor, I would often sit next to a reporter for two or three hours combing over a story, discussing it, polishing it. As a teacher, though, I bring home these 100 paragraphs, full of both flaws and potential, and spend two or three hours reviewing them, marking them up, grading them. That, alas, is just a minute or three with each student's work. I sent these students in pursuit of a perfect paragraph.