Roughly, geek culture has always been toxic masculinity by the back door.
You can get perhaps the clearest insight into this by looking at geeky films from the 80s before they started to bury the unpalatable stuff. "The girl" is the reward. The geeky hero (a boy/teen/manboy) gets to win by virtue of geeky skills. Often, humiliating one dimensional "jock" bullies through gained abilities is a payoff too (cf: the Neverending Story, scaring the bullies into a dumpster with a dragon).
Geek culture more broadly, including the adult programmer-gamer culture, has long believed of itself "we see ability, not appearance" but (1) this has always been untrue in reality, it was racist and sexist and still is, and (2) the things the culture has valued as "winning" have never been different in fundamentals from the mainstream of toxic masculinity - money, women, possessions and power all seen as more or less fungible commodities.
What you're seeing now is the reaction of angry white men who are profoundly frustrated at receiving "less than their due". They blame women, they blame minorities, because they should be winning - are they not the very pattern of a hero, a young white man with geeky interests? And yet inexplicably they are not. (It's very explicable, geeky skills aren't special.)
Anger turns to attempts to put things "right" with terroristic murder.