Companies making DRAM have no incentive to make the best products theoretically possible, they just want them good enough to not get many returns and avoid the risk of a class action lawsuit if a significant pattern of problems appears.

Avoiding returns for ECC DIMMs is a harder challenge when they are used in an environment where the server will have a management system that tracks errors over all time and when there might be a network management system tracking all errors over all systems.

Avoiding returns for non-ECC DIMMs is easy when a few errors per month won't be noticed by most users who assume that Windows always crashes anyway.

Has any DRAM company tested chips and made non-ECC DIMMs from the ones that have lower quality?

As an aside are the 2^N*3 sizes of DDR5 DIMMs (like 24G and 48G) made from chips that had errors in one section and got reconfigured to have 3/4 the capacity to not use the bad parts?