I think it's that usually ESL mistakes make sense. Generally it's going to be because they generalized a rule that doesn't apply in that particular case, or tha

I think it's that usually ESL mistakes make sense. Generally it's going to be because they generalized a rule that doesn't apply in that particular case, or that they've used a construction from their native language that is different in English. Whereas native speakers do weird things like using "they're" for "there" as I mentioned in another comment. Obviously you can still understand how that mistake happens, but it doesn't feel logical in the same way that many ESL mistakes do.