So true. Writing is highly technical and very difficult. Just before I started at my state university, it added a writing test that all students had to pass before receiving a degree because employers complained about the lack of writing skills. Several years in, most people were still failing on their first try.
Unfortunately, writing doesn't have debugging tools, tests and output for feedback to let you know if what you put together works. Rather, you need someone who is a good writer to provide honest feedback.
Also difficult is that developing good writing skills requires good instructors / mentors. I have had too many writing classes with instructors who would give praise for just about anything. All of my instructors in my first year of taking writing classes told me how great I was. It wasn't until I took a technical writing class in which my first paper came back a mess of red ink that I finally felt like I was learning something. That class was one of the most valuable I have ever taken. She told us at the beginning of the class that few people can write well, we probably won't ever be able to write well either (true for me,) but she would help us become passable enough to get through the writing test.
Granted, most writing classes don't focus on the same items as technical writing. But with as much effort as this instructor put into every one of my papers, this can't be something many instructors are willing to do.
How do you become a good writer and get good feedback? I don't know.
Compare this to many other classes in which the instructor is largely a guide and you do most or all of your learning on your own.
ETA: I think the instructor and the quality of the course is extremely important. Many subjects in college can be setup to be easy to coast through or rigorous. The name on the course isn't as important as the contents.