There two main reasons why that monopoly sellers offer discount prices to buyers that are willing to mail in a rebate coupon:

1. Individuals tend to forget to fill out the rebate, and then the monopoly seller still earns the full value of the product sale. As high as 50 percent of individuals forget to file the rebate
2. The rebate program allows the monopoly to look nice to its customers, and show that they are attempting to work with them on particular issues.