This is a fair point considering the use scenario that you describe. For other website this might look very different: Think of all those small websites for which you had to create logins but that you rarely use. They are a huge risk due to people's tendency to reuse passwords across important & unimportant sites.
For those smaller sites people might not even recognize this system as a traditional login: They simply come back to the site, are asked for their email address if they want to get back to their information, and shortly thereafter they have a link in their inbox to their details/comments/favorites/...
For those smaller sites people might not even recognize this system as a traditional login: They simply come back to the site, are asked for their email address if they want to get back to their information, and shortly thereafter they have a link in their inbox to their details/comments/favorites/...