I don't think it's an immature question. I don't think the poster is dissing OB/GYNs at all, but wondering what calls them to the profession.
I think like any profession, there's something about it they like. There has to be, otherwise who would be in medicine at all? My grandmother was a nurse and will tell you about all sorts of wounds and bodily functions, but she did it in part because she loved being able to administer care and make a difference. Friend of mine is an optometrist and loves disease because it's interesting and she can often make a big impact in someone's life by treating the disease and making them see better.
One of the reasons I love my OB is because she helped me through all the getting pregnant business and sincerely rejoiced with us when I got pregnant and had my daughter.
While delivering babies will always be a profession, there are a lot of malpractice suits and a lot of doctors are getting out of that part of the practice because of it. Some of the doctors at my OB/GYN office no longer deliver babies or deal with pregnancy for financial reasons.