Back then, high speed was considered the end-all, be-all. For an attacker, you got in and out fast enough that the bad guys couldn't find you and get fighters over there. For the F-14, high speed let it launch and intercept missile carrying bombers far enough out that they couldn't launch at the carrier before being intercepted. The wing that allowed such high speed was very poor for takeoff/landing operations (especially when operating from a carrier), so the variable sweep wing was used to allow the aircraft to operate safely at speeds which were practical for takeoff and landing.
The proliferation and improvements in radar systems, surface to air missiles, and rapid effective communications among an integrated air defense system largely negated the advantage of high speed, and avoiding detection (low altitude and, now, low observability/stealth) has replaced speed as the larger factor in survival.
Mike