It was not so much about a lone Tunisian fruit seller whose suicide launched a regional revolt or about social media as an organizational tool for revolution. The honest answer is that historical change occurs when sparks come into contact with kindling. World War I would have erupted absent the assassination of the Archduke Ferdinand, and the Vietnam War would no doubt have started absent an incident in the Gulf of Tonkin. Any spark will do when there is enough dry wood. After decades of misrule, the Middle East was ripe for change.
The more relevant question is less "Why did it happen?" than "So what?" What difference will all these departures make? Looking back, 2011 was a year of great transition — but not of transformation.