I don't think there was a significant event; I see it more as the financial foundation was available there and lacking elsewhere.

Venice and other northern Italian states had the luxury of being busy making money instead of having governments constantly building up a State apparatus. When you look at countries like France and England (who seemed to be at war with each other or internally) the Venetians were able to focus on developing trade routes, banking, and shipping. For example, the Venetians were primarily involved in the Spice trade from the east and getting the items from Eastern Mediterranean up to Northern Europe via land or sail routes. This trade made them incredibly wealthy and given that there was little taxation they had excess of of cash to spend as disposable income and could support the Arts and Sciences as a luxury or a whim. Other locations at the same time did not have this financial freedom.