Someone in the archived thread likened it to Occupy, and there's some similarities in that it was a bunch of disparate upset groups with different but somewhat linked interests unifying around something mostly non-specific, that then had short-term momentum simply from the formation of the movement, then gradually fell apart or sects were co-opted by whoever had whatever interest or people remembered they could harass women without needing a "valid reason" or whatever until it became as recursively himself and himself alone described it, "a movement that exists to defend the reputation of itself." Occupy couldn't get to that status because they prioritized the establishment of bureaucratic process over concentrated action for the most part.
Occupy still exists I believe, even formally, and last I knew was doing actual charity work and such because it had shed all the hop-ons and infiltrators and hijackers. Since GamerGate "existed" purely on the internet there weren't even real world relationships to hold it together. Except in the one-drop rule useful way for people like on ERA.
If there's a connection to the alt-right, I think it's that just as GamerGate was running out of steam, the various alt-right trends started and targeted a lot of the same enemies. So it probably had the appeal of shifting from defending "gaming" to saving "Western society" as a whole from social studies worriers. Unlike GamerGate, it's held together better because of "the leaders" shared interests in maintaining and squeezing it for profit and other personal gains.