It takes years to decades before kuru disease exhibits onset. I highly doubt people could even connect the disease to cannabilism let alone modify their behavior.
It is genetic, we have a genetic predisposition to not want to eat our own kind (like most animals).
The reason is also probably partly non-genetic in the sense that evolved due to real harms like kuru. But more likely conentional disease is a far more likely reason. Virus and bacteria you catch would be particularly good at attacking humans and would cause all sorts of issues.
@Amikke @freemo @freepeoplesfreepress Kosher, and the rabbi blessing the meat, must have been a huge advantage for the Jews in those days. The rabbi would have learned to spot spoiled meat; he was basically a food inspector. And if someone did get sick, you had one person who knew where the bad food came from. Didn't the "blessing" even have an expiration time? That would have been important before refrigeration. Religious duty was the one way to make sure something important got done.
@freemo @mike805 @freepeoplesfreepress also take note of memetic evolution. Cultures that didn't eat human meat didn't get sick from it and so thrived better than those that did, no matter if they realised the connection or not. Similar to how some Abrahamic religions forbid pork, which carried parasites and similar unpleasantries but is forbidden because apparently God hates it.