I think that's a little backwards. Not that understanding the reasons a tradition started isn't good, but rather that, almost by implication if not definition, a tradition is observed simply because it is a tradition. If a practice is only valid or only observed because we understand its rationale, it really falls more into the realm of a precept or a code. The example you present illustrates the concept--it has become a tradition despite the lack of rationale.

It might also be said that trying to connect a tradition to its rationale, divorces it from the very context that makes it a tradition--the society which holds it in some regard...whether that be a whole people or just a family.

Maybe most importantly, there are any number of conventions that may have once been traditions in society and for which the rationale is both good and still eminently valid, but which have fallen into disuse. Sadly.