The big difference is that the overall performance of spinning disks is not much different than what it was 10 years ago. However, a best-in-class 2018 SSD is an entirely different beast than a 2008 model. They are somewhere around 5-30x faster now with significantly better write endurance, wear leveling, and capacity (you can get up to 4TB in consumer models for reasonable prices). The market hasn't pushed for solid state drives replacing bulk hard drive storage, instead it's pushed for much, much faster drives (yielding 1-2 orders of magnitude improvement over just the last decade alone) along with small form factor portable storage (SD cards and USB drives). The technology is there for someone to manufacture slow SSDs with the same capacity as hard drives at around the same cost, but the market demand isn't.