I don't like generalizing often, but it seems like runners rarely are the catalyst of regional-shaking or even world-shaking events and a lot of GMs I meet seem reluctant to run games that stray too far from canon. The CAS cannot be dragged into the current Amazonia-Aztlan War, Damien Knight won't be assassinated, the Redmond Barrens will remain as they are, the rumors of a dragon civil war will remain rumors, and the assassin of Eliot Eyes-of-Wyrm will never be revealed. Unless the canon says otherwise in the future.
Bear in mind I've only been introduced to Shadowrun a few months ago and have yet to run a game. I'm also still learning about the setting, its personalities, its history, and so on. I'm used to running D&D games, where the PCs are often heroes that can make or break communities, nations, or even the cosmos. On top of that, their actions are often recognized. In Shadowrun I understand it's more gritty and realistic, with the runners' actions rarely being traced back to them by the masses. It is Shadowrun, after all, and many runners are just average (so to speak) people with above average skills, scraping by in the mean streets rather than glistening D&D heroes.
I'm not quite sure how to word this question but I'll try my best not to sound confusing. How often do GMs break from canon? How rare is it for runners to be in missions that could very well drastically affect the actions and reactions of power players, whether in the Seattle underworld or the international stage?