This was bound to happen eventually.
Now Dorkly isn't saying that Town Portal scrolls aren't an incredibly convenient way to get out of hell and sell off your extra stuff. It''s just that eventually the forces of evil are going to get curious about that glowing blue circle floating down the hall and send someone to check it out. Honestly I'm not sure why they hadn't thought of this sooner, seeing as they always seem to have the damn things on hand.
And thus fell Tristam. Might as well stuff a crystal in your head.