They make a good deal of their income from advertising and services in the EU; have facilities, offices and data centers there; most have daughter companies in the area.
If those facilities, offices, and data centers are owned by the American company, then perhaps Germany should be looking into laws which permit that instead of trying to make other nations' corporations behave by their laws. You can't even _do_ that in China, you have to partner with a Chinese firm to even have that kind of presence there. If Germany wants that level of control, perhaps they should institute it.
There's no inherent need to permit a foreign corporation to own land and an effective business; force them to incorporate in Germany, in which case they can be regulated. If they haven't already, in which case they can be regulated, and this whole conversation is stupid. But it's stupid anyway, because this is what corporations do, and it makes more sense to control them from that angle.