You don't see a White People Museum because, in the US and Europe anyway, that is the default: they are all white people museums unless otherwise stated.
Well, yes, because those countries / continents are historically white. Just like an African museum would be "black people", since Africa is historically black.
And, okay, to really shut this one down, what would you say to a "White History Museum" in Africa? That's a real exception to your hypothesis!
There would not be a problem with a "White History Museum" if there was enough of an historical presence of white people in that place to support it. I don't know enough about the history of African countries to know if there is one that meets this criteria. The same could be said for any "non-default" minority "type" anywhere.
>if there was enough of an historical presence of white people in that place to support it.
Who has the authority to establish that threshold? Seems quite arbitrary and problematic. White History Museum in South Africa? What about Zambia? DRC? All have a white historical presence, and in places like Zimbabwe, an argument could be made that the culture has suffered a certain persecution (I am not taking a side on this argument here).
And, okay, to really shut this one down, what would you say to a "White History Museum" in Africa? That's a real exception to your hypothesis!