Why Does Michael Porter Recommend Expanding the Customer Base of an Organization

Why does Michael Porter recommend expanding the customer base of an organization in terms of the Shared Value creation framework?

A) Doing so could yield significant business opportunities that could improve the standard of living of the poor.
B) Doing so is the best way to ensure that shareholders have the most legitimate claim on profits made by the organization.
C) Doing so could be the only way to meet stockholder expectations in a highly competitive market.
D) Doing so will help to prevent the inclusion of more nontraditional partners into internal firm value chains.