Final answer:
Focal firms source externally usually because the product or service is non-core, can be purchased inexpensively, or the supplier specializes in the product or service. The option that does not fit is that the supplier offers the same product to competing firms, as it's not a typical reason for sourcing decisions.
Step-by-step explanation:
Focal firms typically source from external suppliers for a variety of reasons. These reasons include the fact that the product or service obtained is non-core to their business, meaning they do not specialize in it, or that the product can be purchased more inexpensively than it can be produced in-house. Additionally, external suppliers may have a specialization in providing a certain product or service, offering unique advantages such as advanced technology, specialized skills, or economies of scale that the focal firm cannot easily replicate. However, the reason that does not fit among these choices is that the supplier offers the same product to competing firms; while this may be true in some cases, it is not typically a motivating factor for the focal firm to source externally.