It means “the manufacturer realizes they won’t get the price they charge from other channels from you, so is willing to settle for the PR and tax benefits (and whatever residual cost is still charged) rather than nothing.
> I mean in many cases the product is still profitable for them at the reduced rate, but why settle?
Because for a customer who would pay nothing if their only choice was to get the drug at full price, settling for a reduced price (especially when you also get a tax deduction, and some PR benefit from advertising the discount for the needy) is more profitable than not settling.