I think we're talking at cross purposes here.
Microsoft got burned badly in a comment on this thread, because some contractors effectively wanted to upgrade their contractual status after working there for a while. That led them to update their HR policies to make sure there was no such confusion.
For what it's worth, I am pretty sure that Google still provides cafeteria access for food to the cafeteria work, obviously after service hours.
Another thing to bear in mind is that this is an HR policy for Facebook (I can't speak to Facebook and the actual policy).
They don't really have to make sense, HR policies are there to shield the company from any possible liability and/or the possibility of the body shop's company getting their contract terminated. The spectre of the Microsoft lawsuit is probably likely to forbid certain practices for contractors, direct or through a hiring agency.
Also, for most restaurants, you're not allowed to take food home from the serving line after your shift. If you can take food home from the serving line, that (in the company's perspective) tends to create a perverse incentive for making more food and driving up supply costs for no benefit to the company.
There are many different perspectives for different companies. Simply saying that you've not encountered anything like this is not an indicative of general industry practices. Also, you were contracting directly with the company. You were probably paid better than the food service workers. If you're making under 20 an hour, the incentives for you to sue are far greater than if you were extremely well paid and should not rock the boat.
Finally, if you're spending all your time onsite working for just one employer for extended hours and periods of times, even if you have a contracting company between you and the company, if you do it for long enough and get enough benefits, you can claim that you were actually an employee of the parent company. Sort of like a common law wife. It makes sense that you would want to put up an even higher wall between you and third party contractors.