It was due to Deng's radical ideology - now in retrospect, almost equally radical as Mao just in the opposite direction - that economic development trumps everything, including national security. 造不如买,买不如租. Y-10 was only the tip of the iceberg.
It was not until the late Hu era, 25 years later, that China got actually serious about strategic defense and started the ball rolling for Xi.
This is why when people say that Hu was more "moderate" I just 呵呵 and let them know that Xi is just continuing Hu's last policies - SCS, Yaogan, hypersonics, ASAT and ABM.