Matthew Poole and continuators on Numbers 31:10

10 And they burnt all their cities , wherein they dwelt, and all their goodly castles with fire:

Partly to blot out the Name and Memory of so lewd and vile a people; partly least any of the Israelites should be tempted to settle there, and so be discouraged in their progress to Canaan; and partly least they should be possessed by other people who might prove as bad Neighbours to them as these would have been.