hashkafah philosophy - Why does there have to be a written Torah?

I’d like to ask the opposite of this question.

There, the OP asked why we have a distinct Torah SheBa’al Peh; wouldn’t it help to disseminate the Torah better if everything were written? Answers brought there range from keeping a portion of the Torah unique to the Jews, to fostering the Rebbe-to-Talmid relationship, to helping prevent dispute, and more.

I’d like to ask the opposite. Why is there a Written Torah at all? Because of all of the positive benefits to having an Oral Law, why is anything written down at all?