I thought we were talking about correctness, not going shopping for more-error-prone DIMMs.
And I wouldn't say faster memory is necessarily more error prone. But it doesn't really matter, because non-ECC products have to have extremely low error rates to be viable. Even if a speed is at the high end of "extremely low", once you add ECC you'll have an exceptionally solid component.
ECC isn't popular on desktops because Intel, which supplies the overwhelming majority of the processors for platforms that use DIMMs, doesn't support ECC at all. As such, the market for people who can actually use ECC in a desktop (much less would want to) is very small. The only reason unbuffered ECC DIMMs are even on the market at all is because low-end servers use them.
The real reason ECC is not common is because it is perceived as unnecessary for desktop workloads. Software crashes and corrupts data all the time because of bugs, not bitflips. Most consumers care so little about their data that a single hard drive crash will wipe it all out anyways. Why spend 12% extra on memory if consumers hardly see any value from it?