Jefferson knew correct grammar and so could knowingly violate it to achieve a desired effect. Students lack this kind of pinpoint control over their writing. They didn't make these mistakes on purpose. They made them because they don't know any better. They blunder about the snow-white pages like early Arctic explorers searching in a blinding blizzard and with a broken compass for a nonexistent route.
Many experts say it is at least partly television's.
I myself learned grammar through some such process of literary osmosis. Reading can repair a lot of the damage done in the past by poor teachers or a student's own laziness and inattention. Clear writing has become increasingly rare, a lost art, like scrimshaw or persiflage. A colon, semicolon, or even a dash would have sufficed. As punctuated, the headline turned the professional basketball season into a question mark, and the news into gibberish.