The Buccaneer stayed subsonic to excel at low level

Why was the Buccaneer subsonic if it replaced a supersonic strike aircraft concept?

Its low-level penetration mission valued stability and efficiency at extreme low altitude more than supersonic speed.

A successful supersonic predecessor might have pulled the requirement toward higher top speed, but the Buccaneer's central mission was sustained penetration at extremely low altitude. Flying close to the ground or sea demanded stability, structural strength, and efficient performance in dense air. Those qualities mattered more than briefly crossing Mach 1 at altitude. The subsonic design was therefore a deliberate optimization for the strike profile, not evidence that British designers were unable to pursue speed.