Because ‘idol’ and ‘icon’ are not neutral words — they already carry a judgement, and ‘image’ does not.
The chapter gives the reason exactly: those two terms “are considered pejorative in the context of Judaism, Christianity and Islam, whose orthodox sects condemn ‘idolatry’ or the worship of ‘idols’ or ‘icons’.” In English, the word idol almost never appears without the shadow of idolatry attached to it — a practice those traditions condemn. So to call a temple sculpture an ‘idol’ is to describe it in the vocabulary of people who disapprove of it.
India's own classical texts never used such a word. They used mūrti, vigraha, pratimā, rūpa and others to designate images — often statues — used for worship in temples or homes. None of these implies falseness. ‘Image’ is the English word that matches them: it says what the object is, without saying what you should think of it.