People keep forgetting that this FS was designed by Apple for use in their appliances.

Apple devices, save for their least sold model (MacPro), in their least sold product line (Mac) are consumer devices with no ECC RAM. Most people don't know what ECC RAM is, most don't care, and won't pay more for it.

For Apple, it doesn't make sense to switch to ECC for system memory, however, if they implement storage ECC at block level in their SSD controller (Apple designes their own SSD controllers), they can obtain the same functionality at much lower cost (only flash controller RAM needs to be ECC).