Copy paste of the first comment on that Reddit post:

"So I dont know everything either, but I can give a decent synopsis.

Haachama and Coco (streams 10ish hours apart on the same day) both brought up analytics on stream, and mentioned Taiwan as having a decent follower count. This angered many Chinese nationalist fans, who proceeded to cause problems on social media and BilliBilli, the Chinese equivalent to YouTube.

To save face and let the tension die down, Cover suspends Haachama and Coco for three weeks and leaves the issue there. Thing is, problems escalated as many Chinese viewers (from here on I'll just say "antis" to save space) continued making a fuss, with certain ones (including the people behind the Hololive Moments clip channel on YT) wanting Coco to receive more punishment. I dont know specifics, but I've heard some people think she did it purposefully to keep pressure off of Haachama, as her stream came after and she had been suspended before. However, this hate could also be because of how Coco is, IMO, the most American/Western centered member of HoloJP, due to her constant English, jokes about Hololive USA, and beliefs that she is from America. Point is, people are still pitching a fit.

Well, time goes on and both girls come back to overwhelming support, but we aren't out of the troubles yet. Cover states that they had rules against political comments on stream, but they had forgotten to enforce certain rules. In addition, antis are still spamming in both Haachama and Coco's chats, and Coco has issues with Anti-bots to this day, though they have decreased with time. In addition, word starts coming through that members of HoloCN are having problems with Cover, but most of this is unknown. Almost all HoloCN content was strictly on BilliBilli, with the major exception being Artia on Twitch. Girls twitters start getting hazy, Artia makes some comments about how things may change soon, but a lot of not knowing beyond that. Eventually, Artia and Civia have an impromptu stream where they talk about going independent, but they dont know a lot beyond that. Few days after, Cover sends out graduation announcement on Twitter and dates for each girl, essentially stating that HoloCN is going to be shut down completely. This seemed quick, and was described as sudden by most people who talked about it. As far as we know, some are still going to continue Vtubing, but likely with new models and no association with Hololive.

At this point in time, there's isn't a ton of concrete evidence on why Cover outright ended HoloCN. Most people believe that the issues with Chinese Antis was an on-going thing, though I'm not sure of that. Also, Cover seemed to have a growing interest in a Western audience, with translated clips, idols speaking English, and HoloEN all being wildly successful. This could be an extra reason to pull out of China, as many Chinese nationalists have negative opinions about the West regarding certain... disagreements. I'll leave that tangent there. To further this issue, people have dredged up evidence that shows several of the HoloCN talents have expressed nationalistic views online, with some even bringing up very anti-like opinions of Coco during her suspension. However, I cannot guarantee the validity of this, I have only seen vague references to it.

Hope this helps, and sorry if I missed any major points.

TLDR, Haachama and Coco talk about Taiwan, Chinese antis get triggered, Haachama and Coco suspended and return, Chinese antis continue to raise hell, Cover pulls out of China (possibly related possibly not), we get to current day."