Media mail is the lowest priority of any mailing class. Basically it only travels if there is room on the truck; if the truck is full with Express, Priority, or First Class, they take precedence and the media container sits in the PO until there is room on a truck. That info straight from a very good friend who works for the post office after I asked why it took over six weeks to get a padded envelope marked Media Mail from NYC to OKC that had cancellation stamps from WV, FL, TN, TX and AR on it. She was more surprised that it had been stamped at so many of its intermediate stops than the time it took to arrive.
< ETA don't be surprised if your media mail package takes a very long time to arrive; chances are good that it will arrive quickly but there is the possiblity of it taking many weeks >