If I had to take a guess, it would be because Jesus cursed them with an extra hole, and it is their ultimate subconscious desire to have it filled so they can finally be fully human. The problem is, of course, that this whole can only be filled for a temporary period of time, physically, so the problem is keeping it satiated while there is nothing to plug it with. So women have to create something to metaphorically fill their hole, and since women have never been good at creating art or at the sciences, they turn to that which is easy to create: lies, deceit, and dishonesty.
I think my theory is pretty solid. Indirectly, lies come from imperfection, and all deceit and dishonesty flows from the gory hole between womens' legs. Am I missing anything?