Xanthos & Letoon

Herodotus tells what the Xanthians did when the army of the Persian commander Harpagus entered the plain of Xanthos: few as they were, they marched out and fought; when they were beaten back into the city, they gathered their women, children, servants and possessions on the acropolis and set it all on fire; then they went out to battle once more and fought to the last man… Why would a city choose its own end over surrender?