[pklo]

They were trying to avoid oligarchy, where few powerful families would monopolize the power. It worked remarkaby well, actually: Venetian Republic lasted 1000 years, served as a bulwark against western expansion of the Ottoman empire by running an effective combination of trade engagement and military projection, and was arguably a shining light of western civilization for most of that time. They were done in by the rise of nation-states and loss of income from their Eastern trade, not by failure of their system.