They were negotiating their way up from zero paid sick days per year.
It was the temporal global exception, not the rule, as the worldwide norm was working people to death for most of history. Companies would gladly give their workers zero benefits if they could get away with it.
Unions sent a couple of the big car makers into bankruptcy. They've sent all kinds of companies into bankruptcy - the idea that anything they are suggesting is good by nature is about the same as suggesting communism is good by nature. Sounds pleasant, doesn't work.
Communism and Capitalism are actually quite similar in a sense. Neither of them works well in their purest form, both lead to formation of an oligarchy (party elite,billionaires). Most livable countries in the world mix them in form of free market social democracy.
Yet companies have flourished under that model for decades/centuries. Employers and governments have plenty of levers to make sure workers have no choice but to work while being underpaid.
It goes both ways, unfortunately. Industry in general couldn't exist without laborers, and it has a long history of brutal abuse and horrific, dangerous working conditions that killed and maimed many.
I think it's a cultural problem. We aren't far removed from a time when the general business model was to coercively work people to death to extract every penny of value from them, and that mindset hasn't completely been lost. Workers are callously discarded, not at the doorstep of bankruptcy, but at the first hint that profits might not grow as fast as they could.