Giving birth on back in hospital bed, not optimal position for human birth... why is it most common?

We did not evolve to have our legs up in the air, and be laying on our back.... why is this the most common position for women to give birth that I've seen?

I know midwifes & dulas will discourage this position, and encourage supported squatting, or being on all fours... etc.

But why do Medical Doctors & hospitals still use this method, when the anatomy doesnt seem to fit with the position of lying on one's back to give birth?

Amiya:

This question has nothing to do with a quest to be desirable.
Male dominance is undesirable to me! :P

Excellent question. I don't have a great answer, but I have a good idea.

The same as why men went on a crusade against 'witches' (being midwives, thinkers, womena who could read) they decided in their infinite wisdom Men Know Best. Same reason why so many "doctors" give c-sections rather than work thru the natural process of childbirth. Now Mothers are starting to speak up, and telling doctors what they do and do not want.

I believe I'll be searching for a midwife come my time for childbirth.

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This position is easiest for women who have had an epidural and can't get up, let alone switch positions. However, now a days most doctors let you decide what position you want to try. They give you a questionaire before you give birth and ask you what you are most comfortable with, position wise.

Spreading the legs dilates the birth canal.
While you better not give birth standing that would hurt the fetus, you can not lie supine too since it would raise the intra abdominal pressure thereby raising the diaphragm and compromising the respiration of the mother (also that of the fetus by compressing the vessels). Leave alone thinking of a standing or sitting position.
Remember not all doctors are males and being obsessed with male supremacy is undesirable.

Ummm, I guess 'cause it's less work to lie down than to stand or something. Also, pretty much everything in a hospital is done on a bed or table so I guess that just made sense to them. Just a guess.