Different products. GitHub, more or less, has zero marginal cost for an additional customer. So they can afford to give away their product solely to starve th

Different products. GitHub, more or less, has zero marginal cost for an additional customer. So they can afford to give away their product solely to starve the market for competitors. Supermarkets can't do that because they have a significant marginal cost for each good sold/given away. They can't afford to give away milk to 10 million people to get 500k of them to pay for something else. So the market distortion effects are much more limited in the case of physical goods.