Titan Quest got pirated to hell and back which pretty much put Iron Lore out of business and THQ probably didn't have anyone left to fix it. It's one of the few cases where the developer bitched about piracy and I thought it was 100% justified, people were unapologetically pirating the shit out of that game on almost every forum I frequented.
That's really no excuse. Lots of games get pirated to hell and back. Titan Quest was hardly the exception. Even without piracy, the game would have been a buggy mess on release and word of mouth would have spread through forums and reviews.