They do not have a monopoly on talent and they are actually fearful of being no longer seen as the #1 workplace option for top candidates. Protesting as a Google employee gives you much more leverage than an outsider will ever have (unless you have the $$ to buy off a handful of senators).
For example, I left my country 20 years ago because I wanted a better future and I had no desire nor conviction to stay and try to make that future happen there. Of those who stayed, most had no other choice. However, there's a non-negligible number of people who stayed despite having opportunities to leave, precisely because they are willing to fight to make things better.