Please understand that the only reason why this is being confusing is because you probably downloaded the wrong installer, or misclicked something.
This is the correct one:
All you have to do is download this, run the installer, then click next a few times. Now Cubase and all stock content is installed and ready to use. There’s no word about installing the stock VST instruments in the manual because that’s really all there is to it, there are no additional instructions to follow.
Keep in mind that these forums aren’t the official Steinberg support form, most of us are users helping other users. The same applies to pretty much all other DAW companies. For official support, log into your MySteinberg and check the “My Support” tab. That’s how that other guy who had the same problem as you managed to fix his issue.
Simply downloading the correct installer should make your VST instruments show up though.