Ask HN: Why do some sites show the normal landing page although I'm logged in?

When I access sites like www.intercom.io, www.segment.com or www.google.com/analytics, I see the normal landing page, although I'm signed up and logged in.

In order to see my personal (logged-in) page, I have to click on "LOG IN", "Dashboard" or "Access Google Analytics" (but I don't have to reenter my password).

What's the reason for this approach? I'd assume that it should be as easy as possible for the user (i.e. immediately show my personal, logged-in, page).

Thanks