Or, you could just ask "Why aren't people happy?". I don't see how IQ could make you happier. Smart people are not as smart as they think, they usually perform better because they're overspecialized.
Now, emotional intelligence, that would greatly influece your happiness. The hurdles you're talking about are emotional, not intellectual.
usually when people talk about emotional intelligence, they mean Big 5 Agreeableness plus Openness, which can be measured. If your hypothesis is correct there should be data on the potential correlation between those traits and self reported happiness
There is a lot of data on the Big Five and correlation with subjective well being (self reported happiness).
Extraversion, Conscientiousness, and Agreeableness are all strong predictors of higher life satisfaction and positive emotions. High levels of neuroticism are strongly associated with lower life satisfaction, and openness is mostly neutral.
- There is a strong positive correlation between "Openness" and IQ (some people even claim that "Openness" is actually some weak version of an IQ test)
- There is a small negative correlation between "Extraversion" and IQ
The other three Big 5 traits are basically independent of IQ.
Now, emotional intelligence, that would greatly influece your happiness. The hurdles you're talking about are emotional, not intellectual.