this is because you have set the Lookup value to use the emailaddress column of your users recordset.
on your page, you should have a form with a text box for the user to enter their email address and a button to submit the form.
On the second step of the Email Password server behavior, In the login details section, set the Look up column to the emailaddress column, click the Lightning bolt next to lookup value and select the email address form element.