When trying to select Marketing Suspend Cause as an attribute for a change data value flow step, the field is not available within the pick-list.
The Marketing Suspended Cause field is a system managed field. It will update based on the program of the individual action that updates the Marketing Suspended Cause field. It is not possible to update this field manually or via a smart campaign. It is possible to create a custom field that you could populate with the value of the Marketing Suspended Cause.