Hades was far in the Underworld, Hestia had just left, Demeter was not skilled in battle, and Poseidon had blatantly stated that he would stay neutral. The Goddess of Law had not returned for many years, and the God of Sun along with other deities were basically unable to decide the outcome. All of this was telling Zeus just how thorny the enemy before him was.
Of course, the situation had not reached its worst, after all, it was easy for gods to rank each other, but hard to determine a victor. If his foster parents insisted on taking action, then Zeus would have no choice but to temporarily avoid the sharp edge. Once Hades and the Goddess of Hearthfire realized the commotion here and gathered the power of all the gods, the scales of victory would ultimately tip towards him. However, if things truly escalated to that point, the Divine Court, established for no more than a hundred years, would also become a complete laughingstock.
