I belive it was mostly an accident of fate, but Pedro did say that Downed Tapir lacked the signs of big human cities that usualy drove away the mythicals and magical phenomena as a whole so that might be it. And i don't think that Poseidon had any intentions to "make" a new minotaure since he descended to free one not to make another, but as i said he most likely lost sanity and had his fun without giving it that much thought.
And if you are curious about the scene of the juges of Hades, i think it was in chapter 16 when Asterion when to the rooftop to relax.