With hardware where power-off is only controlled by software, battery life is predictable, and large amounts of data like raw video are being persisted, they might have a very aggressive version of page caching, and a large amount of storage may imply that a scale-up of RAM would be necessary to keep all the data juggling on a happy path. That said, there’s no non-business reasons why they couldn’t extend that large RAM to smaller storage systems as well.
People without the "large amount of storage model" need to record video from the camera too.
The justifications I see are to reduce the number of models needed to stock and to keep the purchasing decision simple for customers. These are very good reasons.