I only know one person who does this. She’s African American and from the state of Georgia. She explained it that her slave ancestors didn’t know their exact birthdays, so after slavery ended people would either pick a random day or a whole month or time of year. She claims this is her way of honoring her ancestors. I, personally, just see it as being selfish in modern times, but I’m not black, so I can’t really speak on her rationale.