Why is Karthus' Lore so different?

Link provided of Karthus' Lore. Why is his Lore so much shorter and rather uninteresting than most of the League champions? Most of them have excellent Lore, tying into the champion's history, who they've interacted with, how they became what they are, etc..

Karthus gets four sentences. Four. FOUR. And in those four sentences, there is nothing interesting or anything that makes him unique, other than a few brief discriptions.

pls buff?