Why can't magazines be sent via Media Mail?

Magazines cannot be sent via Media Mail because they typically contain advertisements. Media Mail is designed to offer a lower postage rate for sending certain types of media items, specifically educational and informational content, such as books, sound recordings, and films. However, items that include advertising content or promotional material do not qualify for this service. The intention behind Media Mail is to encourage the dissemination of knowledge and information, rather than commercial advertising, which is why magazines are excluded from this mailing category.