The point of a riot is that if enough other people are breaking the law, you feel like you can get away with it too. A few hours after Martin Luther King was murdered, by future wife looked out the window at her street in the Austin neighborhood of the West Side of Chicago: "Hey, Mom, look! Everybody's getting free TVs. Let's get one!" Her mother nailed the door shut.
Sports rioting traces back at least as far as the clashes between the fans of the Blue and Green chariot racing teams in Constantinople that almost overthrew the Emperor Justinian the Great in 532 AD. The concept of the Victory Riot after the local team wins the championship was largely unknown in the U.S. until the Chicago Bulls with Michael Jordan won their second consecutive NBA championship in 1992, a little over a month after the Rodney King riot in LA.
The Michael Jordan riots caught everybody by surprise, since the accepted narrative of urban riots going back to the Watts Riots of 1965 had been that they were set off by Urban Anger. But everybody in Chicago was happy. And there hadn't been riots when the Bulls had won the year before. The MJ Riots were worst in the 'hood, where a couple of Arab shopkeepers were murdered, but even the exquisite little Stuart Brent Bookstore on the Magnificent Mile was looted by white yuppies who stole coffee table art books. The next year, the cops were out in force on horseback, but there was still a fair amount of rioting in Chicago. But when the Bulls won their second threepeat in 1996-98, nothing much happened. So, there's a high degree of randomness. Plus, there's target hardening. For example, the Niketown store that opened on Michigan Blvd. in Chicago after the MJ riot is a fortress designed to be unlootable.
Now that I think about it, I suspect there would have been riots after the Chicago Bears won the Super Bowl in 1986 if the temperatures hadn't been subzero. There were scary incidents on Division Street, and then during the official Loop victory parade a few days later when it was still no more than zero, a mob charged a high school marching band and bent their brass instruments. Why? Well, the point of a riot is Why Not?
Never having won anything, Vancouver (a.k.a., Loserville, North America) has no tradition of the Victory Riot. It does have a tradition of the Defeat Riot going back to the 1994 Stanley Cup Final. I suspect, however, that some of yesterday's Vancouver rioters are undergoing an agonizing reappraisal of this whole riot and post pictures on Facebook idea. For example, this guy with the blond crewcut who was photographed setting a police car on fire. My guess is that the police really don't like you setting their cars on fire, and therefore will find him.