I mean you said it yourself: if you have terabytes of data, BD isn't practical.

I feel like this is all just two totally separate use cases. Nobody wants to burn 20-40 BDs per TB, just like nobody wants to use a tape drive (or maintain a RAID array, or whatever else) to back up 500GBs of family photos and tax documents or whatever.

At some point the volume of data dictates what solutions are practical.