The Reason for Quantum Fluctuations in the Early Universe?

Quantum fluctuations arise out of the heisenberg uncertainty principle. In empty space, in vacuum, you have virtual particle antiparticle pairs popping into existence. These two particles collapse back into nothingness before time window closes. But why is it? That's a deeper reality that we still don't know quite very well about. So quantam mechanics, quantum physics, is still very mysterious.