Alright so we seem to agree, my theories aside, that Kuru only happens when eating the infected.
When you say "It happens more often in cultures that practice cannibalism on the regular" I assume you are talking about other than the Papua New Guinea tribes? Can you tell me which groups you are referring to so I can look them up? Thanks!
I don't know of any modern cannibalistic societies outside of PNG. It is banned there like everywhere else but they still do it a little. Despite the lush forest the soil in PNG is not the best and not terribly productive so the people there are always short on food and that is one reason they culturally practice cannibalism, that is a lot of meat to throw away.
There is a lot of information about CWD which is a prion disease that affects deer species in North America if you want to learn more about them. Even that is not entirely understood.