In the last days I've noticed few accounts having "Please delete me" in their profile, and their last visit on this site was around 6 months ago. I wonder who should delete their account and why didn't do this?
Just marking your profile with "please delete me" is not enough, you also need to contact SE and ask for deletion. So maybe those users didn't do that. Or maybe they copied their profile to other sites, but only wanted to be deleted on one site.
User deletion is a process that has to be manually initiated by an SE employee.