Here's a riddle: how do these EVIL GAMER BROS know that they are talking to a woman who is playing an online game? Some games have voice chat, but for most games it is not really necessary to play the game.
The answer is that these women out themselves as a woman in some way, where it is easily avoidable and unnecessary to engage in the actions that would out women as being women playing games.
Most likely, they are seeking attention, similar to what this 4chan post states.
But rather than adapt to the environment, far too many women demand we change the environment to accommodate them. So we get content like this, as if it is a major problem that men need to address. A waste of time, of course, as the people doing the "harassment" can be safely ignored or blocked. Who cares what some idiot says on the other end of the microphone? His "threats" or "harassment" can't actually do anything. He is just like a small yippy dog: very loud and annoying, but not a threat.
Gaming is indeed a space mostly dominated by men. And there are some men who will trash talk and say some crass things. The 12 year old saying "I fucked your mom" on Call of Duty is a well known meme, and one that most men understand to just not fret about that sort of thing or any other trash talk.
But women who are unaware of this universal phenomenon come in and act all offended that "there are harassers in online gaming!" Yep. Just do what the men do and ignore or block. Problem solved.