Generally it has to do with scale. If you make something that 200,000 people buy and your marginal cost is low you're going to make a lot of money. If you work

Generally it has to do with scale. If you make something that 200,000 people buy and your marginal cost is low you're going to make a lot of money. If you work in elderly care you can only provide care for a handful of people you won't make much.