Why does a melting pot of all skin colors have history months and celebrations of all skin colors but white?
Two reasons. First, until recently there were two melting pots: One was the normal one we think of about America (consensual and gradual, including almost all races), the other was just for Africans, and was done by force and quickly through the Trans-atlantic Slave Trade + Suppression of ethnic beliefs of slaves. This second melting pot created black slave culture out of individuals from many different cultures. Black slave culture later became a couple of cultures over time, but these cultures were largely walled off from mixing with other cultures until relatively recently in American history, and some parts lingered even longer. Only in recent generations are they starting to mix, and this separation will take awhile to fix.
The other reason is that there are some people who hate the idea of the melting pot (or as they call it assimilation, which is wrong). These are called leftists (and also the white identitarians) who want to emphasize differences, and trying to set up this POC thing, and like setting up ways to celebrate the skin colors to attack the melting pot.
But as for ethnic celebrations, those are different, and white people have those as well (like St Patrick's Day). They are actually part of the melting pot. You basically end up with bastardized versions of these that everyone celebrates. This is also why calling it assimilation is a leftist lie. It's not that people just are absorbed in, the dominant culture (American) takes something from their culture and adds it to its own. This is what the melting pot does.