Why do I have to log in again every time?

You don't. If you select "Remember me" on the login screen, you will be logged in automatically every time on that machine. Just make sure that you don't click "Log out" at the end of a session, since this will log you out on all machines and require an explicit login next time. Also, make sure that you bookmark the following URL, to go directly to Scrumwise: https://www.scrumwise.com/scrum/