I think that's an interesting point. Do you have a source for your statement, that most of the research happens post mortem?
It makes sense to me that non-lethal cases wouldn't be discovered, as it's probably prohibitively expensive to screen for non-lethal/dormant infections. It could also be that the progression is so slow for most people, that they die from unrelated causes before the disease becomes a problem (this is pure conjecture on my part)
The first promising blood test for mad cow (vCJD) was developed in 2016. Prior to that, "The only current method to diagnose vCJD is to perform a biopsy or a postmortem analysis of brain tissue." (NIH 2017).
It makes sense to me that non-lethal cases wouldn't be discovered, as it's probably prohibitively expensive to screen for non-lethal/dormant infections. It could also be that the progression is so slow for most people, that they die from unrelated causes before the disease becomes a problem (this is pure conjecture on my part)