Doing some research into D&D lore for a project, I took a dive into history of Gnolls. Many are critical of their modern potrayals as spawn of demon lord of Slaughter, Yeenoghu, literally bursting from hyenas that feed on cadavers of his victims. But before that....they did not have an origin at all.
So it turns out that before Yeenoghu, Gnolls worshipped Gorelik, a Hyena-like demigod who has interests only in hunting with his small pack. The thing is, he did not make them either, he merely mentored them for a while after finding them somewhere, and in his hunts across multiverse helped them spread to all worlds. And then he left once he got bored with them, unwilling to rule his own pantheon of Gnoll deities. Between his aloofness and irresponsibility and LACK OF AN ORIGIN STORY, it's little wonder Yeenoghu took over. Before he showed up, Gnolls were trying to even switch their own panthen for that of Giants, but were told to eff off.
There is ONE setting that gave Gnolls origin in days of early D&D, and it's Mystara. Gnolls on Mystara were created as shock troops of Nithian Empire, think fantasy Egyptians. The reason why modern versions don't acknowledge this origin is that Nithians apparently made Gnolls by cross-breeding GNOMES and TROLLS! As their other famous creation - Troll-Hobgoblin-Ghoul hybrid, Thull - can attest, Nithian pun game was immacullate.
So the current origin flat out making Gnolls demons come from the fact WotC is too embarassed to explain how this
was actually created when this
was in the room, going "nice".