Fall of the Eldar

The Eldar had such dominance of the Galaxy, they started to lose interest in menial tasks.

As these are Elves, cue sodomy and masochism. So much sodomy and masochism they fucked this charming specimen into existence.

Cue Galactic scale lulz.

Thus the Elfdar are now a fractured people. Some survived through hiding in a webway-city where said sodomy and masochism is not just acceptable, but encouraged, or noticing that the debauchery was getting out of hand and left long before the Fall to live hard lives on Death Worlds/floated away in living spacecraft, many of which did not escape in time, or dancing around the webway with their patron Cegorach.