Similar to the cloak-and-dagger stunts pulled by the Israelis, what Pakistan did was observed but never stopped actively, which is why the end result was successfully achieved. It created the stability in the region due to MAD.
What is stopping actively? What power could justify active movements then considering the polarized world without consequences?
After all, there were efforts made in the cloak and dagger world to stop the technology from transferring. You make it sound as if Pakistan had the blessing of a godfather whereas you dont provide much proof to that.