As the husband of a woman who went in expecting to give birth naturally but ended up having a C-section, I think I can answer this. The mentality, some internally-driven, some external, is that a vaginal birth is the "right" way to give birth; women have given birth this way throughout the 50,000-odd years of recorded history and for hundreds of thousands of years before that. Women want to give birth the way their mothers gave birth to them and their grandmothers gave birth to their mothers. A C-section, especially an elective one, is considered "cheating". "At least try to do it the right way" is the pervasive mentality.
My wife had a birth plan, several pages long, detailing how she wanted the process to happen for our first child. She had also spent weeks watching the various reality/documentary shows on giving birth (which of course get to cherry-pick the stories that make for good TV). The biggest point was that she wanted to deliver normally. She was on the fence about an epidural, having her water broken artificially etc, but was sure that she wanted the baby coming out of the birth canal.
The moment she was diagnosed pre-eclamptic, that detailed birth plan went out the window. The delivery date was scheduled for the day the baby hit full term (at 37 weeks), and because the baby didn't get the memo, they induced with pitocin (which immediately produced massive contractions that resulted in my wife begging for an epidural), broke her water artificially, let her "try" for 18 hours of unproductive forced labor, and when an ultrasound revealed the baby was trying to come out nose-up against the pubic bone (an orientation that has only a 10% success rate), her OB said enough's enough and wheeled her into the OR. I came in only after she'd been draped and opened, and sat by her head the entire time. I felt like I'd been thrown backward in time to the era in which I was born, where my mom's "old-school" OB had directed my dad to a chair in the corner, and if he moved he was banished to the waiting room, "where he probably should be anyway". I didn't even get to cut the cord. We were both a little disappointed, her more than me (tempered by the perfect little girl we came home with), and now that she's pregnant with our second, she's that much more determined to have a VBAC.
The more extreme of the natural-birth advocates say the rise in C-sections is a conspiracy; the dramatic increase in percentage of babies born by C-section in the US (and indeed the entire idea of giving birth in a hospital in the first place) has not been mirrored in other industrialized nations, and yet the U.S. has higher maternal mortality rates than most of these countries. Therefore, C-sections (and hospital births) can't possibly be seen as "safer", and so there must be another reason (the linked documentary poses many possibilities, from C-sections being billable to insurers at higher rates, to doctors wanting to end their on-call shifts on time).
There's a little "correlation implies causation" in those arguments; there are other factors that can be causative. Increasing maternal obesity during this same time, which in turn aggravates conditions like maternal hypertension and pre-eclampsia that make OBs want to deliver early (meaning induction), is one of them. Increased maternal age in the U.S. also contributes to "high-risk" pregnancy status that has higher C-section rates. Patience is another factor; I dunno about other mothers, but when my wife hit 9 months she was very much "over" being pregnant. This can influence decisions regarding induction and elective C-section; when the doctor suggests it for medical reasons, it seems more palatable than waiting around on bed rest. Induction itself is also targeted; forcing a mother's body to try to give birth before it's ready requires intervention after intervention, some of them (like pitocin vs epidural drugs) contradicting each other in a downward spiral leading to C-section.