User blog comment:Dragonzzilla/Champion Themes and Purposes/@comment-24826890-20140421014456/@comment-24857138-20140424030013

Xerath says he is chained because of his lore though. He was trapped by the most powerful mages of his age in the sarcophagus that he busted. However, he couldn't totally bust his prison, so he wandered for awhile till he found nexuses. He discovered that if he drained enough power from them, he could break what remained of his prison, but the summoners wouldn't let him unless he fought in the League.

Also, Syndra is a (nearly)omnipotent champion and she doesn't have a single quote about being restrained in any way.