For the fixed database roles such as db_datareader, by default the role and a schema of the same name are created. The owner of the role is "dbo" and that role owns the same-named schema. What would happen if I made "dbo", directly, the owner of the db_datareader schema and deleted the db_datareader role?
What are you trying to achieve? Typically you wouldn't be changing system created objects like this, and that schema won't have any objects in it anyway.