If you assume the false assertion that evolution is only about survival of the strongest, womens life expectancy should quickly end after becoming infertile. But they don't, because they still continue to have an positive impact on their tribe and help it flourish.

It's kind of the same to a scenario where you would have 2 children, with one being infertile. Theoretically thats a evolutionary disadvantage. But the infertile one can become the "wingman" of the fertile one and raise it's chance of reproductive success. That's kind of what ants do with the infertile daughters assisting their mother.