The new campus location of Northwestern Polytechnical University is remote and has inconvenient transportation. There might be various reasons for this, but it's definitely not due to the national defense confidentiality reasons as some people have claimed.
Taking the 'Seven Sons of National Defense' as an example, here are the transportation methods from their farthest campuses (excluding Harbin Institute of Technology Shenzhen) to the city centers:
Beihang University to Tiananmen Square: Metro Line 8 + Changping Metro Line (40.5km)
Beijing Institute of Technology to Tiananmen Square: Metro Line 1 + Metro Line 9 + Fangshan Metro Line (38km)
Nanjing University of Aeronautics and Astronautics to Xinjiekou: Metro Line 1 + Metro Line S1 (16km)
Nanjing University of Science and Technology to Xinjiekou: Metro Line 2 (7.5km)
Harbin Institute of Technology to Central Street: Bus Route 91 (7.8km)
Harbin Engineering University to Central Street: Bus Route 105 (6.3km)
Northwestern Polytechnical University to Zhonglou: Metro Line 6 + Bus Route 333 (36.8km)
As can be seen, the other six universities either have convenient transportation or are reasonably located. None of them are like Northwestern Polytechnical University.