You mean "reason" in the sense of "why" and he means reason in the sense of "logical conditions". The why is an interesting question, what environmental or other factors provided an advantage in a plant containing this chemical, or was it a non-important side effect of some other change. It is interesting, maybe not easily knowable.
Hope this clears it up. I may be wrong, but I get annoyed when I read comments that are negative without an explanation, so I thought I would attempt to shine some light.
A similar story exists around the discovery of LSD (LSD-25 was just one in a sequence of lysergic asid that was synthesised by Albert Hoffman) – it was years later that Hoffman decided to revisit the compound, thinking... "There must be something there..."
It's all likely coincidence, but there exists (especially with plants, such as those that produce DMT, and Psilocybin) that we have evolved together.
I wonder about the evolutionary reasons for its emergence. Does the plant influence the Human so that the Human protects and nurtures the plant? When did Humans begin altering South America? 15,000 years ago? More than enough time for the plant to adapt.
It's a strange feeling to ingest a hallucination producing organism. I remember being 19 years old, in the 90s, being given mushrooms. I spent the next several hours sitting at a tree stump feeling myself sink into it, feeling merged with plants around me. I remember thinking a lot about the juxtaposition of the natural with the concrete and brick and asphalt just a few hundred meters away - and wanting to tear it all down. Now, decades later, reading the woman's experience, I wonder if the fungi had somehow manipulated me.