Because there are only twelve days of Christmas, there are only two Sundays after Christmas if the 25th falls on Wednesday through Saturday. For Sunday, Monday and Tuesday, there is only one intervening Sunday before Epiphany. But, if the 25th is on Thursday through Saturday, then the first Sunday after Christmas is supplanted by the feast of Saint Stephen, Saint John, or the Holy Innocents. Which means that we only celebrate both Sundays after Christmas when the 25th is on a Wednesday.
Which it is this year. Just a little bit of liturgical trivia.