Perhaps it was the drive of, you know, a WAR, along with:
a) The ability and willingness for the entire populace to get behind a common cause
b) The resources of the entire country and economy thrown at it, because, you know, possible death and all
c) They could be build by various levels of skilled workers using hand tools, not necessarily CAD/CAM/CNC operators, programmers, etc. Far easier to throw manpower at it.
And yes, the F35 et. al. are all vastly more complex, though it makes one wonder if perhaps a larger number of non-multirole flyers might be a better bet, as we could turn them out quickly, in different versions (see F14) for different uses, possibly populating those barren Brit carriers somewhat sooner.
Please understand that I have nought but the utmost respect to those that answered the call to produce these and other machines on both sides of the pond.
As to the Apollo program, replace WAR and DEATH with "COMMIE BASTIDGES."