Redirection on LJ

If I click a link that takes me to Facebook and I'm not logged in, I get sent to a login page, and after I enter my username and password, I get redirected to the page I was trying to view. A bunch of other sites do the same thing. On LJ, it just sends me to the home page. Why is that? I don't know programming, but shouldn't that be reasonably painless to put in?