After defeating the enemy, why should anyone proceed to worship their gods?
Ramban: Due to the severity of the Isur, 1 the Torah tends to warn against it at every opportunity, even when it appears superfluous. It inserts it here, to warn against it even when, after entering Eretz Yisrael, we would find the Cana'ani idols already made and ready to be worshipped.
Seforno: In order to appease them for having killed their adherents. 2
Since acknowledging it is akin to denying the entire Torah, as the Gemara states in Chulin, 5a (Ramban).
Which is presumably why Amatzyahu (king of Yehudah) did precisely that, after defeating Se'ir and capturing their gods - Divrei Hayamim 2, 25:14 (Seforno).
What are the connotations of "ve'Lo Sa'aseh ke'Ma'asehem"?
Rashi (in Chulin, 77a) and Ramban 1 #1: This is an additional Pasuk 2 prohibiting 'following the customs of the Nochrim' (such as divining).
Ramban #2: More likely, after warning against worshiping it in a way that is Derech Kavod (such as bowing down to it), it is a prohibition against worshipping it in the conventional manner, but which is not done Derech Kavod. 3
Who writes that perhaps this is what the Pasuk means.
See Vayikra 18:3.
Such as defecating before Ba'al Pe'or and stoning Markulis, even if his intention is to disgrace Pe'or or to stone Markulis (Ramban, citing Sanhedrin, 61a, which comments on the Pasuk in Devarim 12:30).
