The sign-up process for Discourse is more complicated than the sign-up process for a Mailman list.
It has been said many times that for every extra field or step people must take completing a form, half the people who start the form will not get to the end of it.
A Mailman list only asks somebody for their email address and then it auto-generates their password. There is no need to choose a username or fill in any other fields.
For communities who run Discourse but want to offer a Mailman-like mailing list experience, users have to manually go into the preferences to enable the email mode of Discourse.
It would be nice to have a single sign-up page where people only see the following:
- enter your email address
- choose the sections you want to be subscribed to (much like choosing which lists to join on a Mailman server)
and everything else will automatically be set up in Discourse email-mode.