It's just that there is a lot of thought wasted solving a derivative problem that could be avoided by continuing to use a simpler solution to the first order problem. This is classical overengineering. At the same time, any good solution to the coffee problem will likely have to find a tuned balance between a number of traits and they will be different for each person.

There are certain abstract tradeoffs that aren't taken into account in the OP (if I remember correctly). In the case of the keurig machine, it solves the complexity and convenience by narrowing flexibility, increasing expense and maybe sacrificing taste (which are all completely valid tradeoffs). The french press or a ceramic dripper maintain the flexibility, expense, taste and minimize complexity at the cost of convenience.