ECC could have been common, if there was a meaningful CPU support for. Intel basically did - "you need Xeon to do exactly what an i7 does + ECC, it just costs 5 times more... We just fused the ECC part of memory controller of i7, so buy Xeon."
The entire discussion is about why ECC is not common and why ECC matters. There is no technical reason for ECC to be uncommon aside purposed market segmentation.
Of course, there is no intrinsic availability of ECC udimms for the retail market currently, however that does mean ECC has no use or benefits for a small extra production cost.