Well you see, gamers tend to be single and have few friends due to the fact that you don't meet many people sitting in your house screaming the N word at people online.
Studies of social species that also exhibit monogamous pair-bonding (especially prairie voles) show that in both sexes being unpaired increases cortisol levels, adrenal activity, and stress response to social conflict, but in males it also increases testosterone levels, where as pair bonding and "nurturing" actions decrease testosterone levels in males. In macaques friendship among males also provided a positive effect on social buffering (i.e. resistance to stress arising from conflict).
This works in tandem with the fact that gamers have no physical activities to master as an outlet to instill a sense of control/dominance through which to appropriately and consistently channel those increased levels of testosterone and stimulatory hormones, and thus their free floating frustration and neuroses become easily attached to anyone or anything that challenges them in any way.
These constantly elevated levels of stress hormones further lead to issues like inflammation which induces a sickness response, consisting of symptoms such as depression, anxiety, lethargy, decreased pain threshhold, and social withdrawal, which only ensures the cycle will become self-reinforcing.
And that's why gamers are mad all the time!