I guess for many places it was simply that food supplies were never that plentiful, so it's worth the risk to try and make safe something that looks like it could be edible.

If your food supply is plentiful there probably wouldn't be the same incentive. But for most people, for most of human history food has not been that plentiful, so any extra source would have been welcome.

This is probably also true of all the ways we've found to preserve food. When you know the winter is going to be lean it's worth experimenting with things to see if you can eek out out supplies of that little bit longer.

Slight off topic, but I wonder how accurate the references in novel/series "The Clan of the Cave Bear" where medicine man/woman skills are mainly handed down from one generation to next. However also handed down is the skill to take tiny amounts of unknown herbs or potential foodstuffs and observe effects on their own body before working out what to do/how to use to treat ailments etc and add to common body of knowledge.

> There has to be a belief that in the end it will yield a tasty, non-lethal dish that would be worth the trail of dead bodies the recipe demanded.

Experience with other foods where proper prep can make them safe suggests that it can be done. And if a plant is in plentiful supply, that provides motivation.

And you can experiment on animals and captives, it's not necessary to kill your family.