The productivity gains went to either things that got automated (e.g. speciality equipment operator - wages are higher but there are less jobs) or knowledge workers (software engineering salaries have skyrocketed).
The wages in lots of sectors without productivity gains have gone up because they must compete against sectors where productivity has gone up. This is known as Baumol's Cost Disease.[0]
It's not a coincidence that there is a rotating crew of Russian speaking janitors who clean my office building and Spanish speaking landscapers outside my apartment. I'm not discounting that many of them are legal immigrants, just lower skilled and working their way on up. More power to them.
I can also see though how this situation is easily taken advantage of. Contracting firm hires undocumented workers for below market rates and is able to under bid for contracts. Big company fires their in house workers to save money and hires the contracting firm. Big company then gets the advantage of undocumented labor wages without the liability.
Wages are a function of supply and demand. If the people cleaning hotels had better options, their wages would go up (or hotels would shut down, or ask people to clean their own room before they leave, etc.)