>Now explain to me why my german salary paying a german rent benefits private shareholders in NYC ? Rent doubled in ten years...

It's simple supply and demand. Your city doesn't allow building many more units even though demand is high and growing; this greatly increases property values, and creates a potential for big profits for investors. A company of private shareholders in NYC sees this investment opportunity and buys properties up so they can reap the profits. You probably also have some relatively weak tenant legal protections, making it easy to raise rents.

If you don't like it, your city should allow more construction. But western cities don't want to do that, because of NIMBYs, "neighborhood character", shitty zoning laws, etc., so we get what we're seeing here.