Maybe it's some kind of taboo or curse in the story. Something bad might happen if you do.
Perhaps there's a powerful magic or rule associated with her name that forbids it from being spoken. It could be a mystery that's part of the plot.
It could be that saying her name summons a dangerous force or awakens an evil entity. Maybe it's a key to unlocking a terrifying secret in the story.
It could be that the story has a strong emotional impact on people. It has created such a connection with its audience that it's impossible to just make it disappear. For example, a love story that has inspired generations. People keep talking about it and it lives on. So, they say 'you can't kill the story'.
Perhaps it's due to privacy settings. The owner doesn't want it to be shared in that way.
Manga has this charm where it can hook you with its creativity and the depth of its plots. Maybe it's the way it presents emotions and adventures that makes it impossible to say no.
Maybe I'm just a bit shy and don't want others to see it for now.
Maybe I just want some privacy and don't feel comfortable sharing that story with you right now.
Maybe that name is already trademarked. Some names are protected by law for commercial use, so if it's a registered trademark, you can't use it without permission.
One example could be a whistleblower's story. The person might not want their name said to avoid retaliation from the powerful entity they are exposing. They are doing the right thing by revealing the truth but fear for their safety and livelihood if their name is made public.
Maybe it's something that could cause trouble if shared in the story. Like if it's a trade secret.
They might say it if it doesn't fit the plot. For example, if the story is a mystery and the thing is too obvious and would ruin the suspense.
Hard to say for sure. It might have elements of truth or be completely made up for entertainment purposes.