Doing ECC on-die (as in DDR5) does solve issues related to the storage itself, and the access timing of the array, but still leaves data vulnerable to corruption on the memory bus itself. Memory is indeed the only place were we are moving and storing data and it is commonplace to use zero layers of data protection; everywhere else we have at least one, often multiple, checksums and storage always has had forward error correction for a very long time, regardless of medium. But of course, generally speaking, all data processed by a computer moves through the main memory.