Natural selection optimizes for long term survival of genes. Humans are probably long-lived because we have high maintenance offspring and a survival strategy built around communicating culture, but this only necessitates survival through 2-3 generations worth of time. Anything beyond that won't be selected for.

Same with health, etc. A bio professor once said "life doesn't work perfectly, it just works." There's a lot left on the table because evolution optimizes for the median case over time.