...... and then there is their and there.
But what I think is happening is the widespread use of texting. Students and some teachers often use "texting language" in their work and consequently many students think it is acceptable. Furthermore, in some faculties you can correct the mistakes but are not allowed to deduct marks for poor spelling and grammar. This achieves nothing more than perpetuating the problems this thread is about.
In addition, you can also see misspellings more frequently in television and don't get me started on Americanisms that slowly creep into the language. That can be another thread
Just my thoughts. Clear skies
Huey