the total shipments of SSDs are still only a small compared to the large amounts of HDDs shipped and this is expected to only change on moderate level during the next years. https://www.statista.com/statistics/285474/hdds-and-ssds-in-pcs-global-shipments-2012-2017/

To achieve the same level of exabytes shipped per year for SSDs than for HDDs, the industry would need to invest about 100-200 billion dollars. This alos means that the price per GB of HDD will not be matched with any type of SSDs during the next years, expecially not for the so called nearline HDDs (capacity drives) http://www.theregister.co.uk/2017/05/22/ssd_price_premium_over_disk_falling/