At least, from what I’ve read it seems to be the standard position.
Not that I’d know, but it seems counterintuitive to me. I mean, men are usually larger and heavier, so wouldn’t it be more comfortable for the woman to be on top? Otherwise they’d get squished.
Male dominance, and getting to look at each other.
Maybe.
“You know, if we do it this way, we can both watch television”
I’ve heard going from the back was more “natural”. I guess they mean it’s a better fit. Dunno.
As to the OP, maybe an intimacy thing, so you can look at each other as mentioned.
As a small woman, I do have to pipe up with “Halp, HALP! You is squishing me!” (Not just during sex, even. And yes, I do speak like a lolcat.)
ETA: I often have trouble with it falling out during rear entry. It doesn’t feel so natural to me…just me?
It’s not necessarily the default. The reason it’s called the missionary position is because when married missionaries arrived in Tahiti, the Tahitians were puzzled by the fact that they only ever had sex in that one position. Apparently, the Tahitians were hanging from the chandeliers every chance they got.
It was considered to be the only non-sinful position by the Church(es) for a long time. Not sure why, though I think the penis stays ‘in’ better for a lot of couples in that position.
I agree that other ways can be more comfortable, especially for a small woman.
ETA: Deleted, as i totally misread the question.
An urban legend, dating I believe from the 1960s. It has no foundation in fact.
The “missionary position” is so called not because its use was encouraged by missionaries - there is no record of Christian missionaries every expressing any opinion on this subject - but because, in the 1920s, missionaries themselves used it, and were observed to used it by the Trobriand Islanders whom they were seeking to evangelise. (The Trobrianders, we must conclude, were given to a spot of voyeurism.) The Trobrianders considered the position impractical, probably immoral, and certainly very funny, and used to re-enact it around the communal campfire as an amusement to while away the long winter evenings. Whether the missionaries found the performance amusing is not recorded.
Why did the missionaries use this position? We have no reason to think that they used it exclusively; they may well have employed a variety of positions, only one of which the Trobrianders found at all remarkable.
That’s what all the mirrors are for…
My favorite is rear-entry for the “better fit”.
I almost typed “TMI” but this is The Dope
I don’t know, but my naughty, naughty, ape brain tells me that the symmetry of the raised and pointed legs, displaying… The triangulation, so to speak, is highly appealing and erotic. Maybe, Flower like? It’s just really erotic, the enclosement.
Liz Phair relays the TV-centricity of the position.
See also: Post #3. 
Dunno about squishing the woman but guys are normally stronger- we can support our weight for a longer time 
Wasn’t there a Straight Dope column about some pre-human species who “may not even have mated face to face”? Or maybe that was a “Why Things Are” column. Well, in any case, I always wondered why it was assumed that humans DO mate “face to face.” Can chimpanzees and other non-human primates have missionary-style sex?
I’m sure I have read somewhere that bonobo’s occasionally adopt this position.
You kiss face to face. This leads to sex. The man has tended to lead the way on sexual advances, and his natural inclination is to set the woman down, be in control…maintain a position of dominance and power. He is responsible for insertion, for taking control…and yet, simultaneously, having the woman on her back, relaxed, is also a sign of caring and keeping the woman at ease.
My cynical thoughts always made me think it had something to do with unscrupulous missionaries forcing natives onto their backs, i.e. raping the natives.
Our perfect master seems to think that this entomology for missionary position does not have much basis.
http://www.straightdope.com/columns/read/737/why-is-the-missionary-position-called-that
It is called the “missionary position” to poke fun and the squares.
If you’re still following this thread, can you tell us how you did read the question? Curious minds wanna know.