The major reason, if I had to guess, is that in terms of physics, the Nobel committee tends to award individuals whose research has impacted something directly tangible and useful (i.e. something beyond pretty theory).

For example, the press release for this year reads:

This year's Nobel Prize in Physics is awarded to three physicists who have made decisive contributions concerning two phenomena in quantum physics: superconductivity and superfluidity. Superconducting material is used, for example, in magnetic resonance imaging for medical examinations and particle accelerators in physics. Knowledge about superfluid liquids can give us deeper insight into the ways in which matter behaves in its lowest and most ordered state.

Not to say that theory can't get you the nod, but that's not what the committee looks for as its top priority.

josh you should get the a nobel award
for nowing how to make hyper link.