The theory of evolution is the theory of the survival of the fittest. No superior entity regulates evolution. Evolution itself is blind, deaf and dumb and all what we see today is the outcome of the survival of the fittest.

So why was it so beneficial for humans not to live much longer than 75 years ?(of course there are exceptions, we all know that, on either side of the scale).

Why was the outcome of the terrible fight of the survival of the fittest not 120 years or 200 years, or maybe just 25 years? If dumb giant turtles in "their survival of the fittest fight" were "granted 120+ years" shouldn't superior human beings live a little longer?

And since all factors of existence were bound by the law of the survival of the fittest, in order for 75 years to become established as the most beneficial age for humans, there must have been a fight between human gene groups who died at a huge difference in age.

By that I mean there must have been gene pools who were able to reach 200, 300, 400 years and other gene pools who only reached 20, 25, 50.
Only if there is a huge variety can the war of survival of the fittest start. But never were humans found to live much older than 75 in general. (aside from a few exceptions in Siberia etc. but even here 120 was the max.)

If age was never subjected to this war, human age was pre-determined, but we all know that since evolution has no intelligence of its own, this is not possible.

So how can Evolution explain that our statistical lifespan of +/- 75 years turned out to be the winner in this war of survival?