Because its a giant glacier, largely uninhabited, and fought over by India and China at a time when both were desperately poor and were trying to claim greatness through the ideological prism of military prowess.
At this point, its not worth fighting over. China will never cede it to India for at least another 50 years, or until the level of trade between the 2 countries reaches a level approaching Sino-US trade - at which point irritants like Aksai chin become less important. India, in its efforts to become a global economic power, has no interest in bringing up the issue and scaring off global investors by such sabre-rattling.
Frankly, its best left alone. Yet another hopeless event linked inextricably with the best-forgotten Nehruvian ideology.
Atheism is Myth Understood.