Just because 'something was done that way' like, say, slavery, public hangings, or excluding most persons, of color and women too, from voting does not make it wrong or right.
But really, tradition is mostly the answer to a question that we've forgot (or can't comprehend anymore), and clothing styles are a part of that. Christening ceremonies tend to be held a couple weeks to a month after the birth, largely because prior to the development of modern medicine the number of children who died in childbirth, or shortly thereafter, so why waste a name?