The school system might have something to do with it. My high school English teacher didn't bother with spelling or grammar, other than to allot 15% of our essay grades to "mechanics" - spelling, grammar, punctuation, general word usage, etc. She assumed we would already have learned those basics in junior high. One of my classmates who had gone to the same junior high school as I did (we had a strict teacher there, and I loved driving her nuts by bringing science and science fiction into as many assignments as I could) once asked the high school teacher about gerunds, and she snapped, "Don't talk to me about gerunds!"And I, at the medium point of your two ages, don't recall being taught whether to say either 'he' or 'they'. I rather suspect I wasn't.
When I got to college and started taking English classes there, the instructor discovered that many of my classmates had a dismal grounding in grammar. So she revised the syllabus to include exercises out of the Harbrace College Handbook and told us that unfortunately this would take away time we should have been using to discuss the actual items on the reading list. We would have to do more of that on our own, because she was appalled by how poorly some of the first essays were written.
That's the class in which my first A was downgraded to a B because I misplaced two punctuation marks in my bibliography. The rest of the paper (on Shakespeare's Sonnet 18) was perfect. So after that, my Harbrace became a constant companion both as a student and as a typist. If any of my clients were having particular problems with something, I'd recommend they get their own Harbrace, or take advantage of the free tutoring sessions in the library.