And this is when they are not actual employees so there is at least legal cover. If Google made them employee it would be 100 times worse.
Mind you, I am not somehow advocating that Google must not hire them. From a culture/ country other than America, I see people can be treated with respect but not paid lot of money mainly because there is not much money to around. But people receiving also understand not a lot of money can be given for certain tasks.
However modern media culture is worst. If Google were to hire full time, I can see headlines "World Richest company pay pittance for back breaking work". And point about job security , benefits would be forgotten.
One can check coverage of full time Amazon warehouse workers on how it plays out. I have never heard a good story about it. Or how other companies hiring warehouse workers doing compare to Amazon across America or world.