Non-Plant based caffeine is a thing. You can chemically derive it in massive quantities, making it cheaper than extraction. I've read that synthetic caffeine tends to be absorbed quicker than naturally extracted caffeine, and is supposedly why some brands bother using both: longevity. Fast upfront hit from the synthetic, then a later hit from the natural. Not something I've ever truly looked into though. For the most part I just drink coffee, so it's never really been pertinent.