And yet, outdated comments are far, far more common than outdated function names.

Because people don't try to squeeze a complete description of what a function does into a single identifier, which is what you you would have to do if you want function names to take the place of comments. I for one don't want to strip all the spaces and punctuation out of my comments so I can use them as function names, and I really didn't want to read someone else's code written in that style.