You most likely use 21st century Internet-enabled book-marketing processes. However, your sales are probably occurring at dial-up speed if you are implementing mid-20th century marketing actions.
You wouldn’t put up with a 1930s-era phone system, or forego the benefits of modern technology, but that is what you are doing when you fail to sell your books to non-bookstore buyers. These could be retailers (discount stores, supermarkets, airport stores) or non-retail buyers (corporations, associations) who could buy in large, non-returnable quantities.
Selling to these special-sales buyers is not a major leap for many publishers. In many cases, you already have the programs in place to do it. Selling to non-bookstore retailers uses many of the distribution partners with which you already work. Begin there, and then expand your sales to build upon your current base, giving you a solid foundation and focal point to grow your sales.