No idea really. I'm not sure many will buy the 1.5TB.
For $2599 (1.5TB and 16GB Ram) you could get a 13" MBP with 16GB Ram and 1TB SSD.
With USB-C and the speed of external drives these days, along with cloud storage, I'm not sure why anyone would need above 1TB on their machine. Unless they are dead set against cloud and external storage. But then I would question the importance of their data if it isn't backed up somewhere.