Because that was the win, in the sense of "victory." One turn – and that was it, the entire game was over for you, and you couldn't stop it.
The fact that it all ended in a rather dull draw, of course, disappointed me. I would have liked to see a final showdown between the surviving city dwellers and the crazies.
Although Hostor was right, the plot was indeed beautiful... But no matter how much I love interesting settings, for me, Mafia is primarily about gameplay.