Matthew Poole and continuators on Deuteronomy 17:17

17 Neither shall he multiply wives to himself , that his heart turn not away : neither shall he greatly multiply to himself n silver and gold.

As the manner of other Kings was.

To wit, from God and his law, Either 1. To Idolatry and Superstition, to which women are oft times prone, and especially such women as he was likely to chuse, even the Daughters of Neighbouring and Idolatrous Kings and Princes, as Solomon did: Or, 2. To other manifold sins and violations of his duty to his people, either by neglect and contempt of his business through effeminacy and sloath, or by oppressing his people, and perverting justice to comply with the vast and exorbitant desires of his Wives.

Least this should lift up his heart in confidence and pride, which God abhorrs, and beget in him a contempt of his people; and least it should encline or engage, or enable him to burden his people with immoderate exactions. They are not simply forbidden to be rich, if God made them so either by the voluntary gifts of their subjects, or by the spoils of their enemies, which was the case of David and Solomon, and Iehoshaphat, &c. but they are forbidden either inordinately to desire, or irregularly, to procure great richs by grinding the faces of their poor people, or by other wicked arts and courses, as the manner of their neighbouring Kings was.