This part is rather easily explained, I think: "how did it captivate so many millions of daily drinkers around the world?" Unlike coffee beans it's trivial to produce, you basically just chop leaves and dry them, possibly with smoke. Unlike coffee there are no adrenergic heebie-jeebies, only a rather strong and 'pure' caffeine high. Supposedly there's a mineral content that'll be nice to the nervous system too. There…
Yeah and from what I remember, frequently cited studies were looking at the combination of maté with tobacco and alcohol, others didn't control for the delivery style. Maté, especially when consumed in a tiny gourd that's constantly refreshed with boiling water, can make the tissues in your mouth and neck more vulnerable to subsequent cigarettes.
On top of that, maté leaves are often smoke dried, which carries some self-evident risks. My conclusion was to get air dried leaves and be mindful of how hot the water is.