I am a union member because I took individual action to become a member. This union would not be as powerful as it is without concerted actions of many individuals.
No single raindrop can cause a flood, but many singular raindrops are required for it to happen.
With enough advertising and lobbying, you can however influence the likelihoods of raindrops acting in certain ways.
(I absolutely agree with you, but I believe that we shouldn't ignore the ways powerful people influence the masses.)
My point was more that people wouldn't join unions if individual action always was all it took.
Indeed, sometimes the role of the union is to get everybody doing the same thing, and provide a safety net for individuals who suffer repercussions for doing the thing.
Corporations respond to our actions, certainly. But in the same way (and for the same reason), we respond to corporate actions. You can bet that every single one of those CEOs in the article is doing everything they legally can to prevent people from "choosing" to go elsewhere. Some are going beyond that.