Do you mean it will kick you off after a while? Or when you open it, you have to manually log in each time?
Like most sites, there is a time limit for inactivity before it boots you. So that's normal.
If you mean the other way, it doesn't keep me logged in either. One possible reason is how your cookie settings are managed. Or maybe the site simply doesn't support this option anymore.
I let my browser hold my log in and password info. That way most sites have all that info automatically entered when I open it and I just need to click the sign in button.