Because military communication uses frequency bands in Hz max in 1-2 KHz and for better relay, in few MHz and even lower so that radio silence is partially maintained for naval usage submarines, otherwise source of any radio wave would be detected and intercepted. hence a Satellite plays the major role for this. There is no facility in Pakistan for this for generating such waves, so they commonly use VHF UHF, which are interceptable at sea.
Secondly the satellite communication is used for long distances, like from Brigade (Mobile backbone nodes) on field or fleet at sea to GHQ in Islamabad only for voice comm. only. Chinese would not want Pakistan to use their tech for this purpose, due to possible Indian, Russian or US , middle man type of attack on their satellite in case of war. That will breach chinese security network also.