Here is an excellent interview with Nan Miller about her findings on the erosion of college writing courses.
One question got at the roots of the problem — the fact that so many students can skate through their K-12 years taking almost exclusively True/False and multiple choice tests. Essay exams are becoming rare, probably because they take too much time to grade.
Back in my own teaching days, I used to have students come to me after doing poorly on essay questions and complain that having them write essays was unfair because their previous schooling had been dominated by the kinds of tests you grade by running them through a scanner. Since those students invariably had very weak writing skills — making the sorts of mistakes you wouldn’t have expected of a fourth grader back when I was in school — it occurred to me that lots of young Americans go through their primary and secondary years in school without having anyone pay much attention to their ability to write in English.
College writing courses are badly taught, but the trouble begins much earlier.