For the same reasons they aren't being charged for massive theft.

For the same reasons corporations in general don't get meaningfully punished for wrongdoing. Corporations are treated with kid gloves in the USA. They can do things that would put an individual in prison if an individual did them, and when caught they get away with a "oopsie doopsie, ok, we'll pay a modest fine and not admit wrongdoing" (after years of stonewalling with appeals and appeals to appeals and motions to appeal an appeal...).

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