Science, marketing, hype? And the proportion of each that contributes to the success or otherwise or lifestyle choice or specific goals, if any.
In the context of one of those coffee superfrappacappamoccacino things with half a ton of sugar and marshmallows and half a pint of syrup on it to sweeten up the gallon of sweetened double cream, washed down with a blueberry muffin and a bagel, the coffee and coconut oil is a good alternative!! Maybe particularly beneficial if dairy is an issue, too. I like coffee (a poor second to tea, mind). I like coconuts. Seems a pretty good idea to combine the two. Not actually tried the actual bulletproof variety but have played about with chucking some oil into my coffee and it just ends up tasting like a coconutty coffee thing, which isn't much of a surprise. I wasn't sure what to expect...as stupid as it sounds!! Doesn't beat cream, a small amount of course, or old fashioned unsexy milk. To my disappointment I didn't perform any miracles nor did I become so cognitively enhanced that I solved Fermat's Last theorem nor did I absorb high velocity ammunition but to be fair I don't frequent war zones when I'm walking my dog, so couldn't really test out that hypothesis. I'm still rubbish at maths, pythagoras being my limit.
Science may suggest benefits to a product but those benefits are exploited and pushed into a publicity machine which grows its own arms and legs. And, the result is that we, as punters, feel as if we are missing out on something particularly as it grows in popularity and is endorsed by many. One of the great marketing triumphs of recent years is plain old bottled water: "extracted from underground volcanic lava untouched for millions of years, pure and fresh".......use by 28 February 2016, may contain traces of nuts, fish and wheat products.
Some science perhaps and some clever marketing perhaps drives bulletproof coffee in my view. But if you like it, it works for you and your goals and your diet is otherwise sound then great. Cup of tea, anyone?