I always wondered about that because I've seen it first-hand, people who can't spell the most basic of words and think apostrophes go before every S and T. In grade school, it baffled me. When you read you don't see plural nouns with apostrophes. The words they can't spell, have they ever read before? When I read and I see a word I didn't know how to spell, I remember it. Forever. At least subconsciously so that if I ever had to spell it, I immediately unlocked the memory of seeing it on paper/in a video game/on TV and how it was spelled.
Now I'm pretty sure it was a mix of me simply having cared about spelling while others did not, my brain processing some types of information a little differently, and everyone in my grade school having English as a second language.
