Presumably the reduced PDF file displays correctly, so there is no problem with Ghostscript producing the PDF file.
As to why the printing process doesn't respect the CropBox, there is no reason really why it should. There are many Boxes in PDF and no real way for a print application to know which one you want to use. As a result printing applications often default to the MediaBox, which you haven't altered (Note that altering the CropBox doesn't change the content of the PDF file, just what is displayed).
Now, if your CUPS chain is using Ghostscript to render the PDF file, or convert it to PostScript, then this can be solved, you need to add -dUseCropBox to the command line. However I'm not a CUPS expert so I can't tell you how to do that. If CUPS isn't using Ghostscript then its probably still possible to instruct whatever is doing the conversion to use the CropBox, but you're going to have to find out what application is involved and alter the command appropriately for that application.