ECC DRAM (not parity but at least SECDED) has been the norm in servers for 40 years, and memory mirroring and other RAID-like schemes that add additional redund

ECC DRAM (not parity but at least SECDED) has been the norm in servers for 40 years, and memory mirroring and other RAID-like schemes that add additional redundancy to entire chips or word lines etc has been a thing for decades too. Even the next consumer DRAM specification (DDR5) will have an internal ECC for the memory arrays. Reliability and yields quite likely mean that even for cheap consumer grade devices it will probably become cheaper to manufacture cells with reliability but covered with redundancy at higher levels (this has been the case for NAND almost since the beginning). For the past several decades, ECC on consumer DRAM hasn't really been required. It's cheaper and "good enough". I'm guessing software and disks (HDDs, removable media, even early SSDs) were almost certainly the biggest cause of reliability and data loss and corruption issues.