Staffing companies also allow companies to amortize and rebate their workers differently. By working through a staffing company you cease to be an employee and become a line item in a spreadsheet. It may not even be "cheaper" for them to hire you through a staffing company without accounting for tax benefits and accounting trickery, which are likely substantial savings. Seriously, though, dude. I've been there. You're a polar bear on a shrinking ice floe. Whatever it takes to give you some jumping room? Do it. There's no happy ending for you here. You know it. Once the job is gone (and you know in your heart of hearts the job will go away) you'll bust ass to get another one. The trick is to bust ass now.
So workers of staffing companies are classed as something like private contractors rather than employees? We have a neologism here in France Uberization (from the company Uber... you probably heard how popular it is here ;) ) - there is a lot of discussion of Uberization of the workforce. Is this what's happening here?