Wow, you are excluding a LOT of workers in your statements here. Most people who work at Google, even the tech-focused ones, are not the type of full-time high-demand engineers who can get a new job at the drop of a hat.
But I'm not sure what that has to do with the question anyway. Unions aren't "intended" only for certain industries or market conditions. They are a means of balancing the power difference between workers and employers. And we see evidence every day that Google and most other large tech employers in the area are abusing the power they have over their workers on a regular basis. "Just get a new job" is not a solution for the vast majority of people who work at Google et al.
But I'm not sure what that has to do with the question anyway. Unions aren't "intended" only for certain industries or market conditions. They are a means of balancing the power difference between workers and employers. And we see evidence every day that Google and most other large tech employers in the area are abusing the power they have over their workers on a regular basis. "Just get a new job" is not a solution for the vast majority of people who work at Google et al.