I'm not sure this is 'official', but in my opinion: "I'm sorry" is frequently used by a person apologizing for their own actions. That's why people respond with "it's not your fault." To clarify, you can use a phrase like, "I'm sorry that happened."

When someone says, "It's not your fault," they're just reassuring you that they don't blame you. It's a polite, reflexive response to your sympathy, common in English-speaking cultures. You can clarify by saying, "I just meant I feel bad for what you're going through."

“ It’s not your fault “: That is an automatic social or cultural response which began in the 1990s. To avoid that response, you can say: "Awww, that's too bad, I hope you recover quick." The response will be "Thanks." instead of “ It’s not your fault “. Many languages use the word "pity". In english it would be "that's a pity". However, this phrase is seldom used, and when it is used, it is usually in sarcasm. By the way, how do you say "sorry" in Neverver language?

I always say, “I’m so sorry to hear that.” It means we are sad to hear they have a problem. It’s much clearer.

Yes it’s a strange thing we British say.