When 8ch became known as the new big bad place of the internet, 4chan lost some of it's boogeyman status, so normalfags got curious, started carefully approaching and then flooded it once they learned it wasn't that bad and they could browse that safe space and get say they "browse the four channel".
Fast forward a bit, 8ch loses it's boogeyman status because the media shifted from 8chan itself into just gamergate, making braindead normalfags forget about it.
Then you get to a few months ago, two major events happened in half, image posting being blocked and the malware discovery. They needed another place to shitpost and to ask about it, so they went to the second most popular image board that they know and know that is safe: 8chan, and there you have it. They go there, see it's not as scary, start shitposting, users don't fucking bully them, they stay there, most likely still posting on reddit and half at the same time, and quality falls downhill.
Honestly, the malware thing was disgusting. They fucking flooded /tech/ (and also the dead board that is /g/ because retards) with "is it safe?" threads. People told them to fuck off at least and they went full damage control "wow, I just wanted to ask a question, this is why I don't browse this shithole, I'm leaving now. I left. Okay. I'm not here anymore. By the way, is it safe?".
Those retards literally posted "I don't care if it's just adware, I just don't want viruses". It really shows the quality of the place where the refugees come from.