I am not an expert on German unions, but I think one key factor is that German unions tend to have company-level decision-making and representation. In the USA,

I am not an expert on German unions, but I think one key factor is that German unions tend to have company-level decision-making and representation. In the USA, it is common for unions to be industry-wide, with little or no significant company-level decision-making authority. These monolithic unions strike at one company or another according to what will most benefit the rest of the union. This means that the union is 'attacking' one company, and helping their competitors, subsidizing the costs to members at that company with money earned by members from the competitors. This is something like blackmail, and is bound to cause animosity with management.