Why did companies stop producing low capacity hard drives (below 500GB)?

I know it's more efficient to make a million GB capacity than a 100GB version, but isn't this the same for all storage mediums! Flash storage still has the low capacity options.

I might be wrong, but even the 500GB HDD is being phased out little by little, which is uncalled for in my opinion.

Clarification:
Given that 500GB HDD has the same price as 250GB SSD if not cheaper, and that 250GB HDD can't cost more than that of 500GB HDD (if they were still made), then by that simple logic, a 250GB HDD would have been cheaper than that of an SSD.