There has been TONS of studies done on morning sickness and what causes it, and there are no definate results as to why pregnant women get sick so much. Theres alot going on in your body though and alot of changes happening very fast...it doesnt seem so absurd that you'll feel nauseated with all that your body is going through. Not every pregnant woman experiences morning sickness though and every pregnancy is different. With my first child i never had it, this time around i was sick the first couple of months daily.
i no im a teen guy but i do no bout pregnancy cuz of my mom and a few ppl i no. Its mostly because when the baby is made, the body is constantly shifting and moving on the inside cuz it knows the baby is going to be there. when it starts changing and such, ur stomach gets moved and u can get what i would think of as almost "internal motion sickness" since everything inside u is moving and udjusting so things get shaken up and u start to throw up from all of it.