I hear what you are saying. I've noticed the same error being made by many people. Another error is to simply leave out a key word. It's very common. My suspicion is that exposure to computer screens all day long, and exposure to radiation from cell phones and routers, has injured our brains in some subtle way. Another possibility -- it could be caused by spell checkers. Bear with me on this one. Before spell checkers, most of the errors in writing were spelling errors. Now that we can use spell checkers and grammar checkers, those errors get corrected (usually -- there's no correction for the difference between "hoard" and "horde," or "mantle" and "mantal"). But suppose some part or aspect of our minds wants us to make a certain percentage of errors. Suppose it demands that we make this many errors, but the spell checker and grammar checker are preventing the errors from happening? What does this part of our minds do? It forces us to make other errors that cannot be picked up by spelling and grammar checkers. Such as leaving out a word. Or spelling "work" when we mean "word" (which I just did, and caught the error). Or omitting a negative.