Maybe you forget that the publishers actually bought the literature at the literature counter every month. So, the WT ALWAYS got paid even if the householder didn't pay for the literature!! It was the publisher that would decide to give the literature away without payment and so take the loss. Seriously, the WT would never give anything away willingly.
And the US government never attempted to tax them. The case had to do with Jimmy Swaggart v Board of Equalization of California where CA wanted to apply their 6% sales tax on the sale of religious literature. The SCOTUS ruled that the tax was constitutional. The WT's lawyers determined that CA and other states would apply this ruling to them because they were SELLING literature (a specific charge was made for each piece to the publisher) so they decided to move to the donation arrangement rather than collecting the sales tax in states that decided to impose it on their literature. A huge strategic mistake that has led them to some of the cashflow issues they currently have.
Name one time you received something from the literature counter prior to the change without paying for it? You can't. Pioneers got a discount but still had to pay.
Amount of profit has nothing to do with it and quite frankly, since the WT is not transparent about their expenses vs revenues, we have no idea what the actual costs to produce the literature is.