OK, I'll admit, I hadn't heard of this holiday until fairly recently. I don't think it was a purposeful slight. It's simply one of those things. Perhaps less time trying to shove Kwanzaa down our throats and focusing on this could have made a difference.
True, right now the emphasis is almost exclusively on the plight of black Americans, and not the work and sacrifice of white Americans who made the holiday possible in the first place. That would be because acknowledging that some Americans who were white might possibly have been good is anathema for many today.
Nonetheless, Alveda King gives a nice boost to the day and why it wouldn't be a bad national holiday. That is, as long as the work and sacrifice of everyone is included in the focus.