If you look at the history of activism at Google, a lot of former organizers have been terminated. The union is there to protect current organizers from similar retaliation.
If I worked at Google and I had some complaint about my health insurance or something, it doesn’t seem like the union would even be the right people to talk to, because they don’t seem to represent the well-being of the workers like an ordinary union.
AWU does advocate for the interests of workers, as demonstrated by this article. It's just that full-time employees don't tend to have as many issues as the temps do.