The GDPR is literally the type of law that Null hates with a passion. I'll post a real close hypothetical, assume Kiwifarms server and Null moved to the EU:
Lolcow A posts a thread about some broad he hates, because she didn't want to have sexy time. Kiwifarms' users start to laugh at Lolcow A for being an idiotic spastic. Lolcow A gets super mad about the thread and demands through the GDPR the right to be forgotten. Null has two options at this junction:
1. Laugh at Lolcow A and do nothing like he is still based in the USA.
2. Delete Lolcow A username, remove all personally identifying information of user including all the quoted replies with his username. This includes the usual doxxing information posted.
If Null does #1 he's open to jail time and obnoxiously large fines from the EU. If he does #2, it hurts Null's ego and probably the website as more moderation will be needed.
Josh could technically say his forum is a historical research place, but the EU would just drag him to court for that. Null's lawyer expenses would go up tremendously. There's a reason 4-5 years back, a lot of BIG American websites pretty much gave up on having EU visitors.
The LA times has even blocked EU people from their websites due to it.