I suppose I have an aural orientation when "in the flow" and write down what I hear in my head. That would explain the frequency of other homophone-based mistakes.
For example, I think "yoo r" as part of a sentence. What ends up on the screen is usually the one that's supposed to be there, but I'm generally already looking at or thinking about the next sentence. So if it isn't the correct "yoo r," I don't always catch it. With "its" and "it's" the visual difference and mechanical "typing difference" is small enough between right and wrong that I very seldom notice the mistake when engaged in writing. ("Writing," as opposed to some form of revision.)
I should add that even if I do catch a spelling or grammar mistake when in the middle of writing, I'll often just keep typing, leaving it for my first revision.
One of my proofers - not a paid proofreader, a volunteer - likes to get drafts "hot off the keyboard". Sometimes before I've done any revision at all.
I like having feedback ASAP, but I really don't need to have "its" and "it's" explained each time.
Anyway ... sorry, I don't know. How hard would it be?