I'm not very familiar to Drupal and there is a behaviour I don't understand. Some image go to example: /system/files/styles/produkt_newsevents/private/, some to /sites/default/files/styles/produkt_promoted/public/.
Well, I found out that the path to /system/files/ is kind of virtual path. It doesn't exist in real. But why is it (it is generated with a view and a image style) gernerated? Is there a specail thing to do in Drupal, that this path private is generated only in this view? Because I don't realy need this virtual path to public Images.
Any /system/files paths are "private" files, meaning the files themselves are served with PHP rather than served via the webserver. As they're actioned via PHP then can then have permissions applied to them - so perhaps only users with a certain role can view them.
This is why the directory, as you mentioned, doesn't exist - it does exist somewhere, it just doesn't have to (and shouldn't) sit in the webroot (else someone could perhaps guess the path directly to it).
As for why some images use it and others don't, this is purely down to implementation. You can set public/ private at a field level - so perhaps your install has just been set up like this?