Why no more champ from

Well read Zileans lore.

Urtistan was attacked while Zilean was researching time-magic in his tower. He didn't notice the attack because the time magic affected his awareness of his surroundings and the attackers left his tower alone. When he came out everyone else was dead already.

And while this lore is subject to change it is safe to say that most of it will be kept as it is,since vel'kozs lore also mentions that urtistan is a ruin and that zileans clock tower is still in relatively good shape.