>>13793596nta, but the difference of the HoloJP/NijiJP situation is:
In the west, HoloEN holds the vast majority position in audience market share, with NijiEN being a distant second at best (or third, depending on how you want to throw Vshojo in the mix, though those stream on a different platform, so there's not as much feeling of direct competition).
Therefore, HoloEN management thinks (rightly or wrongly, but at least from a cold pure business perspective you can at least understand their logic, even if you don't share it) it can afford to basically ignore and pretend NijiEN doesn't exist at all, or to put it in another way, there's simply not much to gain from allowing NijiEN collabs, and potentially something to lose, so the "upside/downside calculation" is as follows:
Upside: how many new people could we gain by allowing a collab with NijiEN? Very little, as probably over 95% of NijiEN fans already know HoloEN exists (hell, a majority of NijiEN fans probably also watch HoloEN both), so there's not much in the way of getting new fresh untapped eyeballs on yourself.
Downside: how many of our people could we potentially lose? As opposed to the NijiEN fanbase, the HoloEN fanbase is probably much more insular, most of them being normie weebs unaware of the wider vtubing world beyond Hololive (probably less than half of the Holo audience does even know NijiEN exists at all, compared to the other number before). As the leading company, it's in your best interest to keep these people in your own bubble as much as possible, and not make them aware that there are other options out there, as some of them could potentially jump ship if they find the new alternatives better to their liking.
Now, in Japan that same logic doesn't work. Niji and Holo are on a much more equal footing there (without going into arguments of "who is bigger" or "who came first", let's just say it's pretty much a duopoly over there, as opposed to the monopoly here), so the strategy of the western Holo branch "let's just ignore Niji and pretend they don't exist, as to not give them an unnecessary leg up" doesn't work there, and would look quite silly in fact because unlike most westerners, nips are indeed already aware that both Holo AND Niji exist. Couple this with the fact that many HoloJP talents also hold longstanding friendly relationships with NijiJP talents (no surprise, given how much of the japanese vtubing scene is recruited from the same old tight NND circles and cliques, where everybody knows each other), and have collabed quite frequently in the past (so much so that the recent development of even the JP branch becoming more insular is noticeable indeed, as it fuels the narrative that when Hololive was small they needed the opportunity to "leech" from the then bigger players but walled themselves off, instead of returning the favor, as soon as they reached their own critical mass)