What exactly was the whole strategy behind running Siren/Muaddib? Was there serious evidence you had that it would win notable levels of Labor defections? There was certainly some resistance to the ticket from parts of the fed base and it may have actually widened Pericles margin by a couple points compared to what a standard conservative ticket would have gotten.
She wanted to run for it, is well respected and has significant experience.
Presidency is a horrendously annoying job that takes immense amounts of time, is insanely difficult to obtain and then once you do, it is easy to get burned out quickly. Therefore, in a situation with a limited bench and almost nonexistant path to victory, it shouldn't be surprising that few are chomping at the bit to run for President, especially in the current era where failed candidates both are self-shaming and discord shamed into oblivion. In a previous era there was not this stigma and you had frequent candidacies by people that helped bring competition and differing perspectives even if there was little chance of victory.
I am not aware of any other motivations, though I can guess some were posited at points in some discord server or another.