Uncle Tom was a Christ figure, in his great charity refusing to hate his oppressors, let alone those (like little Eva or George) who tried to be good and help him within the system as it existed.
Washington promoted negotiation, practical forgiveness, and treatment of the white majority as individuals who could be persuaded to help African-Americans.
DuBois not only rejected forgiveness of the oppressor, but in a racist fashion identified the "oppressors" as an unredeemable, monolithic group that must be overcome with resistance and even violence.
They are in the ascendancy and have been for some time. That's why Washington himself is regarded as a quisling and an "Uncle Tom" -- and why that term has become one of abuse.
That is a very nice, well stated description of the ‘why.’
I thank you.