I was never a coffee drinker at all until I spent a month in Kenya 6 years ago helping a startup get off the ground (ex CTO/CEO lived in Nairobi at the time). I tried the local coffee as was customary (when in Rome...) and because the Kenyans were SO passionate about their local coffee.
I was floored. I got completely hooked, and to this day have not found quality Kenyan coffee here in the USA. The coffee in Kenya is incredible, puts the crap Americans pay $$$ for at Starbucks to absolute shame.
It isn't really about the coffee, specifically, for the lion's share, and this can be said about many consumer goods. It's convenience, a cultivated flavor profile (think McDonald's fries), nostalgia, consistency, the small socialization … and generally a combo of a few of these things.
None of these are inherent to Starbucks, but they've captured a demographic that only needs to be captured once to be captured for life.
So: people paying $$$ for Starbucks aren't really paying for coffee at all, and wouldn't want a superior coffee if you gave it to them in a better environment at half price.