The incentive nobody says out loud
A retainer priced on hours rewards the agency for the client never learning the work. That incentive rarely shows up as bad faith. It shows up as documentation that never quite gets written and dashboards only one side can read.
What changes when you teach instead
Clients who understand the work brief better, argue more usefully, and stay longer on harder problems. The engagement stops being maintenance and starts being the thing only an outside team can do. That is better work and, over years, better business.