Everyone seems to have missed one subtlety: the article only states (with references) that smart people are not happier.
At no point does it say that smart people are less happy (it does mention two studies where in one "lowest scoring" were a tiny bit unhappier, and in another "highest scoring" were happier): the overall tone is that they are equally happy regardless of their intelligence.
And then it wonders why the familiar trait of intelligence does not translate to those people setting their lives up for happiness?
Yes! And the main theory of the article is barely discussed in current comments thread, but to me novel and very thought-provoking: The model of "well-defined problems" vs "poorly-defined problems" and the hypothesis that what we call "smart" is usually being good at solving well-defined problems, but it's being good at solving poorly-defined problems that might correlate with happiness, and being good at solving well-behaved vs poorly-behaved problems does not correlate.
This rings true to me, in that in that model I recognize I'm pretty good at solving well-defined problems, but pretty terrible at solving poorly-defined problems (and currently not especially happy).
That was all new to me as a way of thinking about it! Most of the comments here are about "why are smarter people less happy", which is not what the OP is about, and is more well-trodden.
On the other hand, my experience is that the smartest people I know are very effective at simplifying / formalizing poorly defined problems and then solving the resultant well-defined problems.
At no point does it say that smart people are less happy (it does mention two studies where in one "lowest scoring" were a tiny bit unhappier, and in another "highest scoring" were happier): the overall tone is that they are equally happy regardless of their intelligence.
And then it wonders why the familiar trait of intelligence does not translate to those people setting their lives up for happiness?