When K-cups first came out I, like many older coffee drinkers (I'm 45), was under-whelmed. It wasn't a matter of taste as, being a graduate student, I was content to buy whatever coffee was on sale at the local Krogers. It was that making coffee a cup at times seemed incredibly stupid. "Why would I limit myself to making my coffee 8oz at a time?" Back then I tended to drink 6-8 cups a day and was known to microwave the dregs of the pot at 8 or 9 at night if I was planning on being up late.
Why didn't I use a Keurig coffee maker when they came out? Join me below the Fleuron
The key here is the fact that I viewed coffee as something to be made. As an undergrad at Miami University in the early 90s the only way to buy coffee on campus was in little paper cups from a vending machine. I don't think there was a coffee shop in Oxford, OH, much less on campus.
For many younger people today (I teach at a public university, my nieces are in HS), coffee is something you purchase as a prepared food. You start off in HS buying candy coffees that you couldn't make at home even if you wanted to: Mochachinos, Flavored Lattes, etc. When they leave home or move into a dorm, there's a Starbucks on every corner if not in their building.
Eventually, though, these people look at how much money they're spending each week on Starbucks, or get tired of the hassle of swinging by the coffee shop on the way to work, and they decided to brew coffee on their own. While it's not appreciably harder to brew coffee by the pot in an automatic drip coffee maker than it is to use a K-cup machine, they view the standard unit of coffee production as the cup, as opposed to the pot. And so they get a K-cup and produce a little, non-recyclable plastic cup each time they make themselves their single serving of coffee.
TLDR: Every time you make coffee with a Keurig, an angel gets dysentery.