I always wondered if those people don't notice something is broken.
Given how reliably this happens, I guess the answer is "no". It's also probably a very small number of people, just 1 or 2 with each commonly used name. But still every common name has those 1 or 2.
I wonder if this could be intentional for identity theft or registering an account without using your own mail. Consistently forgetting one's e-mail is a bit weird, but makes sense too of course.
My email doppelganger tried signing up for something recently, so I just went to the site and put in his email address so he can click the link and sign-up.
Given how reliably this happens, I guess the answer is "no". It's also probably a very small number of people, just 1 or 2 with each commonly used name. But still every common name has those 1 or 2.