Because the F-14 was based on the epitome of 1960s tech, while the newer planes were based on 70s/80s tech. There was no slack for upgrades and even maintenance was difficult.
Carrier life is rough on planes.
/not an expert, I knew more about this stuff when I was 12 than I do now heh
(Unless the above doesn't make it abundantly clear, I have little knowledge of aircraft repair procedures)