This was not an abstract issue. The impact was direct enough to motivate many people who rarely do so to act . The issue was non-ideological. Truth in labeling food cannot be said to be a Republican or Democratic, left or right issue. People are tired of being lied to and insulted.
Advertising is, by definition, lies.
Everyone knows it. For once, they could talk back. Protesters included business allies. Even before consumer campaigns got moving, many businesses and co-ops took the initiative, not only to take action, but to encourage their customers to do the same. Everything's faster now.