They can only make a profit if people are willing to buy what they're selling
> Their business is selling hard drives.
Then either they or you are confused. They make the NAS, not the drives. The drives are interchangeable and upgradable, that's the whole point of a hot-swap NAS system.
> I bet a large portion of profits come from that
I think they wanted a large portion of profits to come from that, but most NAS purchasers know that hard drives are a commodity/standardized and won't pay a premium for ... no benefit.