You don't always need to elaborate... Do you think there are many germans exercising their right of return that aren't aware of the holocaust?
In Germany we didnt talk about India as part of the British empire. My scarce knowledge is based on talks with an Indian friend and Wikipedia. Also there are many many genocides unfortunately.
The average German history curriculum tends to cover topics with a German-specific lens. E.g. comparison of single-party regimes will likely involve the NSDAP and SED, colonialism may feature British India in a sidebar but mostly talk about German colonies in Africa, the Berlin Conference, Herero genocide etc. (German New Guinea and the other Pacific colonies seem to get less attention for some reason.)
Its of course, orthogonal to multi culturalism as a ideology, but all the melting pots without a constant economic flame, imploded into civil war (libannon, jugoslavia) or turned into brutal centralist empires (russia, etc.).
"Halfway peacefully" is a bit of a starry-eyed spin on a cataclysmic event that led to the deaths of anywhere from 200,000 to 2 million people.
In general they do because history is human history, not just some country's history, and it would pretty appalling to gloss over genocides of that magnitude.