This is the original article and has better images IMHO.
https://theconversation.com/mad-honey-that-can-stop-your-hea...
https://theconversation.com/mad-honey-that-can-stop-your-hea...
Grayanotoxin containing Rhododendron occur not just in Nepal, but in Turkey, North America, and Europe.
I think there are other plants that the bees concentrate the toxins of.
It must end up being rare for some other reason.