1. The industry is retooling from HDD To SDD, but they apparently can't keep up with demand for SSD's. So the prices are artificially high.
2. Demand for faster, denser, and lower power SSD's are coming from the cloud providers. So rather than incremental price decreases over time, we're seeing the prices are staying the same, and we're getting incremental technology improvements. The V-Nand technology is the hot new thing, enabling 2TB of storage on a single chip.
3. There's no more serious innovation on the HDD's since SSD's will likely eclipse HDD's in 2021.[1]
[1] https://www.statista.com/statistics/285474/hdds-and-ssds-in-...