According to various commentaries it would seem Jacob hid them under the oak tree and also out of sight so that the position of them was unknown to the people In a way hiding them out of sight of the people so that they were unable to locate and use them was as good as actually destroying them.
John Wesley Notes
And they gave to Jacob — His servants, and even the retainers to his family, gave him all the strange gods, and the ear-rings they wore either as charms, or to the honour of their gods. Jacob took care to bury their images, we may suppose, in some place unknown to them, that they might not afterwards find and return to them.
Jacob hid them under the oak—or terebinth—a towering tree, which, like all others of the kind, was a striking object in the scenery of Palestine; and beneath which, at Shechem, the patriarch had pitched his tent. He hid the images and amulets, delivered to him by his Mesopotamian dependents, at the root of this tree. The oak being deemed a consecrated tree, to bury them at its root was to deposit them in a place where no bold hand would venture to disturb the ground; and hence it was called from this circumstance—"the plain of Meonenim"—that is, "the oak of enchantments" (Jud 9:37); and from the great stone which Joshua set up—"the oak of the pillar" (Jud 9:6).
and Jacob hid them under the oak which [was] by Shechem;
that is, the idols, which, after he had broke to pieces, perhaps, he dug a hole under an oak, and there buried them, that they might be no more made use of in an idolatrous way; and he chose to put them under an oak, because it is a tree which often stands many years before it is cut down, and besides was used for religious purposes, and had in great veneration, and therefore seldom felled.
It would seem hiding them under the oak was as good as destroying them