MMA Junkie points out the obvious: The UFC 82 card is too crowded for all the stars to get on:
Right now, Arlovski is the bigger name. He's a former champ, a headliner, and a fan favorite. Even though he's been shut down for eight months, Arlovski has remained relevant and well-publicized thanks to his marketing team. However, he could also be on his way out of the UFC. Arlovski has just one fight remaining on his current deal, which expires April 15. After his next fight, Arlovski is expected to shop the free-agent market.
Looks like Arlovski is going to be on the undercard against Jake O'Brien. Quite the rapid fall for a guy who was once one of the UFC's most popular stars. I understand the decision if Arlovski is insisting on testing the free agent market, but the UFC badly needs heavyweight star power, and I can't imagine why they can't find a way to make a deal with Arlovski.