The current Pantheon is essentially Hades and Apollo putting on a double act. Athena certainly has the brains, but her combat power is not on the same level as Hades and Apollo, so she is nothing to fear. The same goes for Ares—he is simply too weak in comparison.
Hades and Apollo are comparable in strength, but there is a vast gap in their influence. Among their cohort of candidates, only the faction behind Poseidon the Sea Emperor can rival Apollo. That is why Hades has always wanted to make a move against Poseidon, hoping to push Poseidon's candidate into power as soon as possible. Granted, that would mean one more competitor, but compared to facing the pressure of Apollo all by herself, having someone who can keep him in check would make her life much more comfortable than it is now.
Yet what she can figure out, Apollo can naturally figure out as well. Besides, one has to admit that only Hades could pull this off; none of the other Main Gods have the capability. Apollo certainly isn't foolish enough to create a sworn enemy for himself just so that person might feel some gratitude toward him with his help once Poseidon takes power... None of them are simple characters; it is purely mutual exploitation.
Chapter 370