Because there WILL be a wedding! Mark my words, post owl employee... or, on second thought, ministry representative that is working with the owl post. I am RESOLUTE in this proclamation, that my son is madly in love with this muggleborn girl, and against all of his good breeding, has chosen her for a wife! And I, Lucius Malfoy, have had a change of heart where muggleborns are concerned, and am ready to accept her into my arms as my own. Not, into my arms in a romantic sense, you see, but in a fatherly one. A healthy father-in-law/daughter relationship, yes indeed.