I'd assume there really isn't much room for HDD prices to come down in contrast to SSDs since the latter always fetched a premium until the technology started becoming more commonplace.
I think it's simply a matter of physical limitations, we basically reached the physical limit of how hard disk work storing while ssd relie on microchips and we are becoming capable of making more and more circuitry in the same amount of silicon which makes it cheaper
I've bought a used Crucial MX500 250GB for 30€ in 2019.
Last week I got a Crucial MX500 1TB for 45€.
I can get a 2TB for below double-price but I only need 1 TB and I read that it has a different build with lower speed (lower TLC, smaller DRAM or something, I don't know).