>>16267071This graph shows that the "boom" in the west was from June to October 2020.
Since 4chan is more exposed to Japanese web culture than most places, if you only browse 4chan it probably feels like they blew up in December 2019. But to the west at large it's not even close to the summer 2020 growth. That time period started around when the world was starting to lock down, Korone was playing DOOM, Asacoco was at its peak and Haachama was vomiting on-stream. I'd wager that those clips started the summer boom, and Coco's 3D, EN debut, and the Taiwan yab continued it.
As for the winter growth... I dunno. Fubuki Scatman, Korone noises, and Matsuri bandaids?