OK, so I'll give you my take on it...
As far as me, I've only been interested in realistic ob-gyn exams (realistic CMNF medfet) and I believe it's because I find the unacknowledged sexuality exciting. I also like the challenge of turning a normally uncomfortable situation into a pleasurable experience for a female patient. I never got into enemas, diapers, rectal temps, etc because I couldn't envision a realistic CMNF scenario where they would happen.
I like other CMNF situations where the male and female are both attractive and know each other beforehand. For example, strippers normally don't really excite me, but I once went to a strip bar and unexpectedly ran into a woman that I was friends with who was stripping part time. She was a very attractive and was just doing it for extra money, as she actually worked in the medical field full time. That was about as close to the excitement of an ob-gyn exam for me, as I could see her naked but couldn't be intimate with her.
Since I started thinking through ob-gyn scenarios, I began to realize that a woman's feet affect my level of excitement during an exam. I never believed I had a foot fetish, and I actually used to laugh at a friend who had one, as he had a difficult time getting through summers with all the women wearing sandals. A woman's bare feet are exciting during an ob-gyn exam because they represent complete nudity and exposure to the doctor, although a cute pair of ankle socks are sometimes exciting because they represent a feeble attempt to cover a small portion of the body when more intimate areas are exposed.
As far as others, I think some males like the power dynamics of being in control and having a submissive patient, and some females enjoy submitting to the doctor. I can also see a BDSM aspect and how some playdocs might enjoy giving (and patients may enjoy receiving) pain/discomfort during play exams. There may be a voyueristic side for men who enjoy watching other female's exams, as these are normally very private, and some female patients might enjoy exposing themselves to a stranger. Some of the men who enjoy watching their wives being examined may have a cuckold fantasy, as they are watching a stranger touch and inspect their wives' breasts and vaginas, and some women might get excited watching their husbands get turned on by their exams. I've also noticed that some of the people who post in this forum also enjoy enemas and rectal temps, and most of the commercially available medfet tends to combine these with unrealistic ob-gyn exams.
Lastly, I wanted to make the point that ob-gyn medfet appears to be the most taboo and the least popular of all the fetishes. I think it's because it to involves women in a vulnerable position, the fear of acknowledging the possible sexuality of real life exams, and the fear of criminal or civil liability for misconduct. Rectal temps, enemas, and BDSM are for the most part purely fictitious scenarios that don't invoke disturbing thoughts of what might happen in reality. In contrast, most play docs are aroused to some degree, but the thought of their real ob-gyn becoming aroused is very disturbing for most women, and I'm sure husbands would be irate if they knew their wife's doctor was aroused.