Why would I want to do that? I already make many multiple times more than my peers due to my specialized skill set.
I remember my first job out of college. Somehow, salaries got leaked and I was making 40% more than my colleague, in the same position (he sat right next to me).
The difference was my experience and negotiating skills.
'Collective action' as you say just adds a middleman that won't do much for me..except prevent me from getting a raise on my own terms.
Again, no thanks.