The decision was made collectively, i.e., by majority vote. They could have defended Arandor just as easily, even though he mostly talks nonsense, but he's still a pretty good player.
In general, he was just unlucky. In the end, the city played well, but it was also just due to a bunch of random coincidences.
Such a suck-up to the city :\ what kind of maniac is he if he only kills mafia members?
Except the ones we've made