4chan's compromisation came as a consequence of the 2016 election cycle when anons from /pol/ were doing cross-site outreach to reddit communities like r/the_donald in order to spread online propaganda in support of the Trump campaign. As a result, this drew a substantial amount of attention to 4chan from both mainstream leftwing and center right internet communities, which unleashed a torrent of normalfags across every board on the website save for maybe /a/ and /jp/.
8/r9k/ probably hasn't returned to 8kun more likely due to the fact that 8chan /r9k/'s previous board owner, Tyrone Muh Dick isn't interested in recreating the board and reassembling the old communtiy. I'm positive that whatver is left of 8/r9k/'s community has scattered here, to wizhchan or sequestering themselves in seperate imageboard bunkers with their own /r9k/ boards.