Anatomy, we women don't have prostates. Not that I am an authority on anatomy but while women's G-spots are supposed to be the equivalent and I have read that it is possible to stimulate the G-spot through the rectum. G-spots aren't the easiest thing to find even when you are looking in the right opening so I would think that looking for the G-Spot through the rectum instate of the vagina would be like trying to find the Washington monument from Northern Virginia.
I have met several women who really enjoy the anal stimulation of an enema and toys while using a vibrator on the front. The anal stimulation seemed to make their orgasm very hard so I disagree that men are more anally stimulated. There are nerve clusters that run from anus to vagina.
Most all of us were given enemas by our mothers or at least I was so therefore you got the opposite sex angle from the early years. I know that there is one poster here that says her father gave her enemas but I think that would be the exception, not the rule.
I never considered the opposite sex theory but I do know that I wanted to give women enemas from a very young age. This was a result of having mine forced on me by my mother. Would I have had the same fetish if dad had done it. I'm really not sure so I will concede thisa one.
If mothers used the over-the-lap position, a male's sexual organ is touching the administrator's warm thighs. As you know, a female's clit is sorta shielded. Even if the administrator is using the over-the-seat position, as my mother did, the penis is making contact with some surface. Again a female's clit is shielded.
I got mine on the bed and didn't masturbate to the thought of giving enemas for 5 or 6 years after my last. I don't buy this one.
Last but not least, men are more easily aroused.
I don't think so and females can have multiple orgasms one after the other. Guys just can't have more than one or two even when they are 20 years old.
While there are probably others, those are the points that come to my head.