"HCL employee and union organizer Ben Gwin says HCL workers make between $30,000-60,000 a year, and it varies widely." That's really low. I wonder what kind of work they do for Google.
The painfully obvious answer is that the work is low skill. Why? Because the job market in the Bay Area is such that high skilled labor can easily and quickly find more gainful employment. It doesn’t make it better for them to earn less, and a union is one way to group high and low skill labor pool such as the whole can have a better quality of life.
If you're in a bind and need a job, you get placed quickly by one of the firms supplying contractors to the large companies. Since you're in a bind, you accept making a lower salary, which ends up being around 60-75% of the base salary of a full-time employee without any of the other benefits of being full-time.