Regardless of whether people are extraverts or introverts, if they are asked to act in an extraverted way, this improves their mood (for example Zelenski and others 2012). My question is concerns the reasons for why introverts don't engage in extraverted behavior. According to dual process models of behavior (for example Strack, Deutsch, 2014), human behavior is a combination of impulses and more reflective behavior (for example self-control). It strikes me that extraverted behavior is often quite impulsive (e.g. posting a funny picture of oneself on facebook). So, do introverts lack these impulses, or are they too inclined to keep them under control? Is there any research that has tried to disentangle the two processes?
This may not be a perfect answer to your question but it should be of help. Essentially, I think that research on personality suggests that self control (and thus a lack of impulsivity) may be part of the reason why introverts don't engage in extraverted behavior.
According to personality research on arousal , levels of extroversion and introversion are linked to peoples' arousal levels. Extroverts are argued to be under-aroused (in terms of brain arousal) therefore they seek out new stimuli, while the opposite is the case for introverts. Hence as introverts already over-aroused, they are more likely to avoid new stimuli.
While the research you have cited suggests that introverts would actually benefit from seeking more social interaction, the fact that they do not is not particularly surprising as humans frequently fail to act in ways that benefit themselves.