Mainly, many people get off work on that day and just look forward to getting another three-day weekend! The MLK, Jr. holiday is *supposed* to honor this man, who is still suspected by many to have Socialist, pro-Communist leanings; but as with most U.S. holidays, it's just an excuse for time off work and school! Plus it gives the USA a holiday to honor a black citizen, and some so-called "Afro-Americans" *do* speak about Dr. King's "I have a dream" speech. Some colleges and universities host speakers, both black and white, who were involved in the 1960s Civil Rights Movement; but for the most part, as I've said, it's just a day off, with Federal, State and local government offices closed and no U. S. Mail delivery.
Many students of genuine American history - myself included - would rather see black Americans like Frederick Douglass, Harriet Tubman, Sojourner Truth, George Washington Carver and Booker T. Washington especially honored along with their accomplishments discussed in schools and universities on their various birthdays, without necessarily having a day off work and school.
*real* American history, as opposed to politically-correct history