Particularly for systems that are installed as appliances in customer data-centers, where you as the vendor are both (a) responsible for the appliance as a whole to continue working but (b) have little / restricted access to continue maintaining it, RHEL helps you sign long multi-year support contracts for said appliance with the customer while keeping your maintenance costs to a minimum (since the cost of hiring more support engineers then flying them out is going to be higher than the RHEL license cost).
Particularly for systems that are installed as appliances in customer data-centers, where you as the vendor are both (a) responsible for the appliance as a whole to continue working but (b) have little / restricted access to continue maintaining it, RHEL helps you sign long multi-year support contracts for said appliance with the customer while keeping your maintenance costs to a minimum (since the cost of hiring more support engineers then flying them out is going to be higher than the RHEL license cost).