A dish can become traditional because one person repeatedly agreed to make it.

A tradition is often one person agreeing repeatedly. Not a decision anyone made, not a ceremony anyone designed, but somebody who kept making the same thing until it became what the family does. The weight it carries now is the accumulated weight of their willingness.

So two things follow. If a tradition matters to you, notice who is carrying it and whether they still want to, since these arrangements usually end abruptly when the person can no longer manage it. And if you want one, you do not need agreement or a plan. Do the same thing on the same occasion enough times and it becomes tradition on its own.