The presence of off-topic or disruptive posts in a thread that's supposed to be focused on something like Honkai: Star Rail can be driven by several psychological and cultural factors, especially when it comes to forums like 4chan. Here are a few possible reasons why people might post about cuckoldry in a thread about a gacha game:

1. Anonymity and Lack of Accountability
Freedom of Expression: 4chan, especially the /v/ or /vg/ boards, is known for its culture of anonymity. The lack of usernames means users can post whatever they want without fear of personal repercussions. This freedom often leads to a kind of "anything goes" atmosphere where users feel less restrained by social norms or community guidelines.
Shock Value: Many 4chan users thrive on getting reactions, and posting controversial or provocative content, like cuckoldry references, can be a way to provoke others and derail conversations. In this case, it might just be about getting a rise out of people who are there to talk seriously about the game.

2. Trolling and Disruption
Culture of Trolling: 4chan has long been a hub for trolling, where users disrupt threads and derail discussions for the sake of amusement. Topics like cuckoldry, which some people find uncomfortable or absurd, can be used intentionally to disrupt a thread's flow.

"Meme Culture": What starts as trolling or an inside joke among a small group of users can evolve into a meme that gets spread to other areas. Even if it's completely unrelated to Honkai: Star Rail, users may post these memes simply because they've become part of the site's larger culture.

3. Escaping the Topic or Groupthink
Disinterest in the Game: Some users might not be particularly interested in Honkai: Star Rail, and as a result, they post off-topic content simply to steer the conversation in a direction they find more engaging or humorous.

Satire or Critique of the Game/Community: It's possible that users are posting about cuckoldry as a form of satire, either mocking the game or the players who are overly invested in it. Sometimes, people make absurd posts as a critique of the community's obsession with certain themes (e.g., fandom shipping, waifu culture) or even aspects of the game itself.

4. Cultural Context and Popularity of Certain Themes
Subcultures Within 4chan: The concept of cuckoldry (especially in its exaggerated, often humorously crude form) is a meme that’s been circulating on 4chan for years. It has roots in certain subcultures and is often posted in intentionally absurd contexts, including on unrelated topics.

Sexual Humor and Shock Humor: 4chan's user base often embraces sexual humor and shock value as a form of entertainment, sometimes linking topics like cuckoldry with absurd or exaggerated fandom scenarios. This can sometimes spill over into unrelated threads, as part of the site's larger "anything goes" culture.

5. Influence of Meta Threads and "Honkai: Star Rail" Fandom
Hypersexualized Fandoms: Many gacha game communities, especially those surrounding anime-style games like Honkai: Star Rail, have hypersexualized or meme-driven subcultures. Discussions around waifus, fanfiction, or relationships between in-game characters often blend with other aspects of internet culture, such as cuckoldry jokes, leading to off-topic posts that are meant to be funny or absurd.

Jokes About Relationships in Gacha Games: The dynamic of relationships, whether romantic or otherwise, between characters in games like Honkai: Star Rail often gives rise to playful or over-the-top comments about character "ships." These can sometimes bleed into crude humor or references to cuckoldry, which becomes an exaggerated and humorous way of talking about relationships between fictional characters.

6. Echo Chambers and Groupthink
Mimicking What’s Popular: On 4chan, if a certain meme or type of post gets a lot of attention in one thread, others may start to mimic that behavior to fit in or gain attention. If cuckoldry posts are gaining traction in some parts of the forum, it’s not uncommon for others to jump on the bandwagon, regardless of whether or not it fits the original topic.

Conclusion
While it's frustrating for users who want to keep the discussion focused on Honkai: Star Rail, the kind of off-topic posting you're describing can be seen as a product of 4chan's culture: an unpredictable mix of anonymity, trolling, meme-driven humor, and a disregard for traditional conversation norms. It’s all part of the chaotic, free-wheeling nature of the platform, where users often treat any discussion as an opportunity for disruption, humor, or cultural expression, regardless of how off-topic or inappropriate it may seem.