I think it's a combination of their consistent and obvious decline in quality, combined with the fact that most people in this country have been regular customers for at least some period of their life. Very few fast food chains are as widespread and common in small communities (McDonald's and subway come to mind). I don't remember any other fast food chains getting worse almost overnight, but I do remember Tim's switching to much worse bread on their sandwiches, and their donuts going from fresh, to frozen but decorated, to whatever you call the attempted smearing of nearly solid "icing" on top. Are other chains any better? I can't say for sure, but I can say Tim's at any previous point in history was.