While people do send christmas cards, they are typically mailed several weeks in advance. I assume that Thanksgiving and New Years cards function in similar ways, although I have never met anyone who sends either of those so I could be wrong. Valentines cards, however, are sent specifically on Valentines Day or timed to arrive on that day, and since post offices don’t function on federal holidays, delivery would be impossible. Columbus day involves no cards, so the functioning of the post office is irrelevant.
While people do send christmas cards, they are typically mailed several weeks in advance. I assume that Thanksgiving and New Years cards function in similar ways, although I have never met anyone who sends either of those so I could be wrong. Valentines cards, however, are sent specifically on Valentines Day or timed to arrive on that day, and since post offices don’t function on federal holidays, delivery would be impossible. Columbus day involves no cards, so the functioning of the post office is irrelevant.