You're standards are to high. The kinds of mistakes native speakers make are often technical -- not using commas correctly, dangling they're participles, switching affect/effect. And that's because they're transcribing the voice in there head. Annoying to grammer prescriptivists but the meaning ends up being clear and understood.

A'int gonna end up being authors or technical writers for sure but it doesn't get in the way of actually communicating.

And it is highly unlikely that aforementioned group of illiterates are applying for software engineering positions... so I'm not sure how relevant this statistic is.