I might be wrong, but I seem to remember that Toribash relies on a few external resources that are served over http, this would be an issue in moving forward on full https. There might also be a lot of hard coded hrefs that link to http littered throughout the code, although this **could** be fixed with some nice python automation fixer upper magics.
Possible issues with breaking the game client from talking to the site?
That's a few things that comes to mind for why we can't just set up a certificate and bob's your uncle.