Direct Mail Packages Without a Letter Make No Sense

CBeyond sent this piece as First Class Mail with a tracking number in a card stock 9-1/2" x 12" outer and included an Amazon gift card tipped to a one-sided 4-color insert. But no letter.

NAC (North American Communications) sent a fold-out chart (seen on top here) outlining the latest 2014 USPS rates, with nothing else in the envelope.