Learning Impact on Customers

Learning professionals are so focused on employee development, we can lose sight of the obvious point that the purpose of well-developed employees is so that employees can make some impact on customers. That impact could be better customer service, selling something that improves a customer's life, or otherwise helping a customer solve a problem.
Customers pay the bills, so why not measure the success
of learning programs based on customer success?

In other words, customers pay the bills, and we exist (our companies) because of paying customers. So why it is that learning professionals do not somehow tie success to customer success?

Why don't you measure the success of the learning organization metrics tied to customer success? If you do, tell us how. Share your reasons in the comments below.