It grew out of the Sad Puppy movement a few years ago (https://en.wikipedia.org/wiki/Sad_Puppies#2015_campaign https://en.wikipedia.org/wiki/Sad_Puppies#2015_ca

It grew out of the Sad Puppy movement a few years ago (https://en.wikipedia.org/wiki/Sad_Puppies#2015_campaign https://en.wikipedia.org/wiki/Sad_Puppies#2015_campaign, linked to the year that was most organized and has the best description, but the whole article is worth a read) - a right wing anti-diversity voting campaign the Hugos dealt with from 2013-2017. Slating was a group of voters organizing to all vote for the same group of works (or slates).