I would imagine it is to thin the wax so that it is distributed over the media better and will evaporate in short order, leaving the media thinly coated with the wax.

With that said, I've been using the Lyman Green media for 25-30 years at least as it does a nice job of cleaning and polishing the brass and lasts a long time also. It's a corn cob media and it will get in the flash holes, but I clean my cases before I resize and deprime them when I am not wet tumbling.