Consider the following:

If you imagine the standard monopoly practice being to undersell the competition in a price war until they go out of business, consider: what happens when you and your competition already offer products for free?

The answer in this case: have less ads. It’s simple when you think in terms of economic value and not just money. However, that brings up the obvious question: Did monopolies ever work by that way? (Did MS undersell their products? Was Office/Windows ever underpriced?)