Why can't/won't students learn to write?

While I am worrying about writing content, I realize that I am procrastinating actually reading my students' work for some reason. Now I know the reason, which was "reminded to me" a moment ago by a colleague who would tear his hair out if he could over the extremely poor grasp his students have of the English language. It is getting worse, or maybe we're just sicker of it, but college students rarely know how to write. This says to me that they don't do much reading, either. He wants to know if we should make the second tier of Composition a prerequisite for all junior- and senior-level classes. I know, however, that even that won't work, as they don't seem to teach to grammar and syntax any longer anywhere. We'd likely be out of business, as even more students would head for classes that have no COMP requirements. Is this the decline of civilization, or is this the way English has always rolled with the punches?