^Labels tend to become associated with certain attitudes. When enough racists used "Negro" in a derogatory way, African-Americans tried to switch to a "nicer" label, "colored." But then that got contaminated by the same racism, so they switched to "black." And then 20 years later they switched to "African-American." Because the labels weren't the problem, the attitudes were. Changing the labels didn't help.
It's like when the MPAA abandoned the stigmatized X rating in favor of NC-17, which they hoped would be more respectable. Instead, the NC-17 rating was instantly besmirched with the same cultural expectations and stigmas as the X rating before it.