Tasweer is NOT purely a Fiqhi matter, hence you find it being discussed in Kitab At-Tawheed!

Sheikh Najeeb Ash-Shar’abi ḥafidhahullāh said (paraphrasing): The issue of Tasweer is tied to Aqeedah and not purely a Fiqhi issue based on two reasons: THE FIRST REASON: The first act of Shirk that took place on earth was because of two things: 1. Exaggeration with respect to the righteous, and 2. Imagery Allāh the Almighty said regarding the people of Nūḥ: { وَقَالُوا۟ لَا تَذَرُنَّ ءَالِهَتَكُمۡ وَلَا تَذَرُنَّ وَدࣰّا وَلَا سُوَاعࣰا وَلَا یَغُوثَ وَیَعُوقَ وَنَسۡرࣰا } “They said, 'Do not renounce your gods! Do not renounce Wadd, Suwā', Yaghūth, Ya’ūq, or Nasr!” [Sūrah Nūḥ: 23] These are names of righteous men who lived at the time of Nūḥ. When they died, people created images of them as a reminder. But when this generation passed on and the next generation came, they began to worship these images. This is reported in Bukhāri on the authority of Ibn ’Abbās raḍhiyallāhu ’anhu. So, this was the first reason for the appearance of Shirk on the face of the earth; imagery and exaggeration with respect to the righteous. THE SECOND REASON: Shirk is tied to picture making in several ḥadīths. For example, the Prophet ﷺ said, “The people who will be most severely tormented on the Day of Resurrection are those who imitate the creation of Allah.” This ḥadīth is reported in the two Ṣaḥīḥs on the authority hadith of ’Ā'ishah raḍhiyallahu ’anhā. Therefore, the picture maker is competing with Allah Almighty by imitating His creation.