Because he felt he didn't fit the job. Currently (as of September 5, 2022) Carola Schouten is acting Minister of Agriculture, Nature and Food Quality. She does this alongside her other Minister job.
He decided not to take on the job due to a lack of fit. As of September 5, 2022, Carola Schouten currently serves as the interim Minister of Agriculture, Nature, and Food Quality, concurrently performing another ministerial role.