Some of it he intended to publish. There are extensive writings in his notebooks on subjects such as painting and anatomy. He planned to write books on both. His notebooks are littered here and there with ideas for books he wanted to write. But da Vinci had a fatal habit of burning very brightly on a subject only to have his enthusiasm cool as he moved on to a new subject or some new commission. As he neared death he is quoted as considering himself to have squandered his talents and bemoaned leaving so many projects unfinished.
Explanation: so basically because he didn't have enough enthusiasm about it after he found something else to study
