The Importance of Interaction in the Creation of Complex Matter

Neutrinos are different from the other three basic fundamental bits of stuff in that they only feel the weak force. In order to build something out of neutrinos, you'd have to have them bound together by the weak force but the weak force is just too weak to do that. So it's basically not possible to build more complex structure using theweak force. It wouldn't take very much energy to break it apart. Very cold bits fall together to make a bound state and then be very easy to break it away.