Many of these days/months need to be reviewed and perhaps deep-sixed in the spirit of unity. Singling out special groups to be celebrated is un-American.
They were created by presidential proclamations, they can be eliminated in the same way, but good luck getting any president to do that.
What President Trump just renamed African American History Month was created as Negro History Week in 1926. It became Black History Month by the action of President Gerald Ford in 1976.
Any group can apply for a presidential proclamation if enough people sign petitions.