Because corporations have a singular and sole objective which is "to make as much money as possible". That's it. That's their only purpose. This is doubly true for publicly traded companies who are obligated to their stock holders who only want their stock price up.

Privately held businesses might operate on the ethical standards of their owner but large corporations have very little practical, financial, or functional reasons to be good employers. They have every practical reason to be profitable businesses.

Which means, in the absence of some power telling them not to they will do anything and everything they can to increase profits. Google the Triangle Shirt Waste Factory fire for a good example of this.

So the functional idea is that if you value people then companies need to be told to NOT do things like..wage collude to keep wages artificially low, or skimp on safety measures, or hide money from taxes or, I dunno, avoid safety precautions on your trains carrying tons of toxic chemicals because it's cheaper, and who cares if some kids in a small town in Ohio get birth defects?

Some people care more that a bunch of women don't die horrifically in a factory fire, or children don't end up with cancer because a train spilled vinyl chloride in the town's water supply, than they do about a company making an extra billion