We are not "built for it" lol. Humans evolved to have huge brains for thinking and a narrow pelvis for running, and those two things historically kill a reasonable fraction of women. Not so much that the population can't grow, but something like a 1%/birth rate. Roll that dice 20-30 times and you get a lot of dead people.

Mortality aside, pregnancy is incredibly hard on the human body. Demineralized bones, anemia, vaginal scarring and fistulas, etc etc. Whole lot of stuff can wreck your body without killing you.