Spelling?

What is it about spelling that causes so many issues for people?
I was reading a few threads on boards.ie this evening and practically every instance of “their” or “they’re” or “there” was misused.
I know they are homophones, but surely people must be aware of the very important difference between them…
Maybe I’m just old and boring, but I find reading posts (or emails) with this kind of junk sprinkled liberally throughout to be very frustrating / annoying ……..