I don't know why it's different, but unions and employers are not terribly contrarian in Germany. For example, I have seen (edit: a works council, related to unions but not the same) argue for better quality control because they were fearing quality trouble, which would be bad for the whole company including employees. Unions also don't oppose laying off really underperforming employees (but might require a generous severance package) or automation, as long as affected people can be moved around instead of laid off.
Its like the saying that any form of government works well if everyone is altruistic. Maybe Germans or even western Europeans as a whole are just more altruistic than the US? Individualism and distrust of power are pretty core to the mindset of a decent portion of the US going back to colonial days. I'm not suggesting blindly trusting power is a great idea, but perhaps thinking that way, then acquiring power makes you more likely to abuse it.
I think "narrative" is probably the most underrated element in economic theory, probably because it's hard to measure. But it's easy to see: Many American CEOs appear to be only in it for themselves, and as you say US culture is very much individualistic: Always care for yourself first. Compare this to e.g. Japan where kids learn from very early age that everything you do, you do for the community. With these completely different mind-sets the style of cooperation is very different as well.
As a German I can also say that unions and Betriebsräte are not only looking for the employees but also looking that the business has a future. And that's a common ground with the employers, which is why there is not this kind of animosity as in the US. Also, as I said: Even managers in Germany know that the success of the company is a group effort.
Managers in the US largely are concerned about the next quarter earnings so they get their full bonus. This at the sacrifice of the business in the long term because they will have moved on. And unions usually span many states even support multiple sectors of industry, so the failure of a single business often doesn't seem to matter to the union.
