Some people might want to. If I want to backup my data to SAFE I might buy enough to allow me that and spend it all. Not everyone will, of course.
In your theory the capacity will be cheapest early on, so anyone looking to use it should do so earlier rather than later.
My Pi 2 B with 8TB HDD can replace literally hundreds of such vaults. If my setup won’t be economical, yours will be economically catastrophic.