Answer:
Because people do not need a second newspaper, it will not bring any more information to their lives, rather than a second soda can or snack.
Explanation:
The law of diminishing marginal utility states that there are some products or services to which an increase in the consumption will not bring the same utility for the user as the right amount, for example, if you eat a slice of pizza, it will bring certain benefit, you'll be less hungry but if you eat 7 slices of pizza at some point you'll no longer be hungry and it will rather make you sick, in this case vending machines have a higher marginal utility, a person could drink 3 or 4 drinks or take 4 or 5 snacks before it makes them feel sick, whilst a person that buys a person buying a newspaper won't need a second one, even if it is for his/her family, a 5 people house has enough newspaper by taking 1 copy of it.
Other examples of this can be a vacuum cleaner, you don't need a second one if you already have one, or a house buying a second house ain't as necessary as the first one.