Clients are students
Your role in a company isn’t to just be the designer of products; Your role is to be a designer of that company, to help it become the company that has the ability to make the products you aspire to make. Mike Kruzeniski, Jony’s Patience, 20 March 2015
This advice from Mike Kruzeniski ought to be heeded by agencies, as well. You may have a contract that only scopes the design/development of a specific product, but taking on this role comes with some obligation, in the moral sense, to help your client learn from the experience.
The immature may fear training a customer to not need them, but good teachers are not forgotten. A more likely outcome than losing work is that your next project will be more enjoyable and productive.
(It may need to be said that helping them learn does not mean training them. Rather, it means recognizing the journey of learning you are on, yourselves, and including the client in it.)