I can't think of many people who are willing to lug full-sized mobile workstations just for *storage* space. If you need more than 1TB of storage permanently inside your laptop, you're likely an edge case.
Sure, it would be nice if I could have all my RAW files and all my music and my entire TV and movie collections with me at all times, but would I go back to a 3kg monster just for that? What exactly are you lugging around on your laptop?
Apple probably (rightly so, IMO) just doesn't care about the twenty potential customers worldwide that need more than a terabyte of storage in a very mobile laptop. Unfortunate, but understandable... how much money do they stand to make from you? $3000-4000 isn't even a drop in the bucket.