>>536260873
>1-he already has the lore set up. 2-Nasu loves Oberon and doesn't give a shit about Goetia or Batman.
3-Popularity.
Before you tell me Batman is popular, I don't deny it, but Oberon has MILLIONS of merch and he sells out every time. He's a moneymaker. And one of his ascensions look like a girl, so it's more 'safe' than semi naked muscled guy.