> Getting someone to look over your stuff and looking for spelling errors sounds like a simple and easy fix doesn’t it?
There are a lot of people who don't speak English as native language. I, as a non-native speaker learn about very subtle rules of the English language all the time, where the author often explains that even many native speakers are often not aware of these rules and thus write in their own native wrongly. It already occurred multiple times to me that I asked, say, 5 people at the floor of the institute where I work at, about some subtle grammar details in English. All of the persons who I asked were much more fluent in English than me (though not native speakers), but nobody could answer me the questions. I even sometimes confuse English native speakers with my questions about subtle details of English spelling, grammar, or word usage (side remark: it is my impression that native speakers of German are often much more aware of all the subtleties in their native tongue than native speakers of English).
So it is really not easy (even if you have English native speakers to ask) to find someone to proofread your English texts.