Why does our species reproduce in the way it does?

Because it is good enough. Enough humans survive the process and become adults it is not a detriment to the species as a whole. Evolution is all about "good enough" because it is a blind process. If something works it works.

Because it just has. That's just the way we evolved. Pregnancy is stressful on the body, and birth is, too. I should know. Genes have gotten clever at reproducing themselves.

because science from our big brains that kill our mothers allowed those who would not have children to continue their line thus never removing any selective pressures

Life seems to be all about reproducing so one could argue it's pleasurable to encourage us to do so. The pain of childbirth... No clue. God? Lol

Blame it on a woman and a talking snake!