I could go on a long rant about people trying to appear clever when they are not. See also, incorrect use of “whom” and so on.
But the underlying cause is that everyone now communicates in a text based format – emails, internet forums, facebook, whatsapp and so on. All completely unchecked. You read it enough, and you start to assume it’s (*) right.
Go back 20 years and most people’s (**) reading would be limited to books and newspapers and would (hopefully) learn the correct way.
This week I’ve been on a plane where I read a book, and have been following the newspaper coverage of the Brexit shambles; and still reckon most of my reading has come from the unchecked typing of others.
(*) I know this one
(**) yes, I checked, because I have at my fingertips access to the most comprehensive source of knowledge in all of human history.