In Canada it was about goods and services tax (GST). They didn’t want to register or pay it. They could have sold as an all in price and kept it simple for the publishers. They had captive sales. The publishers paid for the magazines whether they placed them with householders or not.
The watchtower organization has “the government is out to get us” arrogant attitude. They could have just collected and remitted the gst and kept the revenue stream from selling literature to the publishers. It was also a win for the publishers as they could count as placements all of the magazines they purchased even if some ended up being given for free.