I don't know of anything older, although it is possible that Animism may out-date Mother worship, which is a little more sophisticated.
I can think of an explanation, but of course since none of us were there, take it with a grain of salt as large as you wish.
Flint tools wear out quickly, and are replaced often. In fact hunter gatherers who live in an area where flint outcroppings are common often don't bother to carry stone tools from place to place, but Knapp them as they need them. However, the "Venus" figure, having spiritual significance, and no doubt taking much longer to fashion than say, an Axe head, would be carried from place to place. Sounds reasonable to me, anyway.