My own speculation is guided by the principle of, no one is in a vacuum from their culture, and no culture is in a vacuum from its historical precedents. Video game industry culture traces its lineage back to when it wasn't mainstream, when it was kind of a niche thing associated with...well, kinda geeky middle-class males. At least, in the United States. It was kind of similar, in that regard, to the history of sci-fi fandom. And so, there can be a kind of trickle-down effect where, even if the majority of members are not sexual harassers, there is a higher-than-expected prevalence of sexual harassment, facilitated by trickle-down probabilities.
I have mixed feelings about generalizing too much about the sexual problems of gamers, especially if we restrict attention to the modern day, but the social deficiency part seems more plausible, at least taking into the account the qualifiers of my previous comment. I don't know if we have too much data about the social competencies of gamers either, so this is the realm of speculation. Presumably, the "geek/nerd culture" that gave rise to the niche of video game culture in its early days had a higher proportion of people with social skill difficulties, introversion, shyness, communicative challenges, etc. than the mainstream members of society.
