Dragged pages larger than source document
The Mac OS does not optimize PDF files the way Acrobat or other PDF generating applications usually do. It may also be that when you drag the page to the desktop is is making a PDF that is really just a wrapper for an bitmap image.

You could try using "Export As..." by right-clicking a thumbnail of a page and see if that results in smaller files. Another choice would be to delete all of the pages you do not want to keep and then save the file.

Here is a decent thread about optimizing PDF file sizes in Mac OS. https://discussions.apple.com/thread/3213814?start=0&amp;tstart=0