What a question!?
As a part of J&K it has historically belonged to us. What's there to occupy in it?
^^^^^^^^
Gilgit Baltistan is as much part of J & K as other parts are including siachen glacier, saksham valley, aksai chin etc because all these areas were part of princely sate of kashmir. as far as siachen glacier is concerned then siachen glacier is either shown as independent identity or part of indian J&K in international maps & not as a part of pakistani kashmir.
In the 1846 Treaty of Amritsar, this region was initially excluded
from the state of Jammu and Kashmir. However, later, the Hindu Dogra
rulers of the princely state were allowed to administer them on behalf of
the British for reasons of access. However, the people of Northern Areas
did not accept the suzerainty of Dogras, who exercised meaningless
control over the region through a British Political Agent based in Gilgit
or through local princes of the vassal states such as Hunza and Nagar. In
1935, the British got these territories on lease for a 60-year period from
the Dogras. The lease was cancelled, as the British decided to partition
the Subcontinent. Afterwards, the Dogras tried to re-assert their political
control over the Northern Areas, but its people fought valiantly,
liberating the region and then willingly acceding to Pakistan a few
months after independence.
The only purpose of Siachen was to show off.
it's like IA could just walk to any place in Pakistan with one hand tied behin their backs 
