
Maurice S. answered 03/28/19
Expert in reading, writing, grammar, composition, and comprehension.
You are correct on both counts. The short answer is that these actors are not expert grammarians. In fact, they fall into a larger category of people which includes math and science teachers, as in my common complaint that, "Math and science teachers aren't English majors!"
Disappointingly, I have recently also been given cause to complain that many English teachers are also not English majors!