It started off with a woman named Zoe Quinn (if that's even her real name) cheating on her boyfriend with several people and it was speculated that because she had a loveual relation with Nathan Grayson, that Nathon had given her game (Depression Quest) a positive review because of that. (unrelated: It was later shown that Nathan's name is in the credits for Depression Quest from all the way back in 2013, before the review) Because of this, people started digging into things and evidence started piling up that several gaming journalism sites were corrupt, and that is when #gamergate started. Multiple sites put out a total of (iirc) 20+ articles within the same day all saying the same thing: "Gamers are dead" which prompted a lot of suspicion. It was later found that they had a secret mailing list where they were colluding together to try to push their agendas, and talk about what they will and will not talk about on their sites. that was pretty much the final nail in the coffin for all those sites.
now several companies like adobe and nissan and colgate have pulled ads out of gawker media (the place that runs a bunch of the sites that were colluding with eachother) and they're losing thousands of dollars, and people are trying to get more companies to do the same