The projections I've seen SSD + HDD will not keep up with an exponential increase in demand. In the next 5 years there is not going to be enough storage manufactured to meet the world's needs, that means SDD manufactures and HDD manufactures win. The cost of storage is going up along with profit margins.
If you're a Google or Amazon where are you going to buy your storage? SSD is at best 6X HDD, if its was only 3% more expensive the big users would still be buying HDD. I've seen forecasts out 100 years before SSD overtakes HDD.
The costs to build and maintain a .013um fab is astronomical, the COO is not constant and in many cases not decreasing. HDD is cheap and fast and the costs SOO is much more manageable for now and in the foreseeable future.