1. Internet communities are built on memes. Shibboleths, call-and-response, signifiers of ingroup status, they're steroids for building a sense of community and belonging. They arise organically and are also artificially seeded by marketers wishing to grow a brand.
2. Livestream-based communities are especially susceptible to this. The environment built is one where memes grow and flourish even against the will of the streamer. Consider the trouble Mori and Kiara had when they tried to move away from the shipping memes, or Mococo has had with her dislike of memes based on mispronunciations of her name.
3. A very long-established meme in Henya's community, dating back to the Pikamee era, is comically pretending to be attracted to anyone but her. When she mentions a friend or family member, the usual response is to ask if they're single. The community has 'friendzoned' the vtuber in a comedic inversion of the usual dynamic between vtuber and audience.
4. We are what we pretend to be. The meme is intended in jest, but if you act something enough, it is hard to keep from believing it on some level.
The time to 'fix' it was when the meme was young. The momentum behind it is too strong to be completely defeated now. It can be pushed back against, such as with the new costume, but there will always be a segment of the Henya fandom that see her as unsexy, even if they would normally be attracted to her appearance. That said, I don't think that even from a marketing perspective this is a problem to fix - as described above, the meme that has caused this is a powerful tool for cultivating her audience, and those in her audience that find her unsexy almost always describe it in an endearing way - 'little sister', for example.
