Most holidays turn into something else. Memorial Day becomes a day for all the dead. Hallowe'en is about costumes, plus candy for children and sex for adults. Not many people think about the Labor Movement on Labor Day. Presidents Day is about buying cars. And don't get me started about Christmas, which has become at least three other holidays. This despite the serious effort of many people to read the correct Bible passages and get people focused on the Incarnation every December, with a four-week warmup.
Martin Luther King Jr's Birthday isn't much about MLK now, any more than bunnies are about Easter. It's not even really about Civil Rights, though that's a bit closer. There is at least a nod to remembering protestors.
What is it now, and what is it becoming? I think it is a merger of Black People's Day and Liberals' Day. Conservatives quoting actual words of King are viewed as unworthily touching holy things. From what I hear at work, I have strong suspicions that it means different things to African-Americans of my generation versus the currently rising generation. But that's a long guess on my part. Others would know better.
The holiday isn't that old, either.