In the past marriage was traditionally more of an owner/property relationship than it is today. I'm oversimplifying a bit, but for much of history a woman and her children were in serious jeopardy without the economic support of a man.
Unsurprisingly, the "obey" part of the wedding vow was more common and taken more seriously. In particular, a wife had little or no expectation of being in a position to refuse to have sex with her husband, nor of preventing him from sleeping with other people if he has the means and inclination to do so.
So a wife's libido was at best kind of irrelevant and at worst a nuisance, given that a wife with a low sex drive was that much less likely to put her husband in the position of spending a big portion of his resources supporting someone else's offspring.
Fast forward to our modern era. Women in western society can earn enough to support themselves and their children if they so desire, so tolerating and staying with an abusive husband is no longer seen as a virtue. According to society's current morals, men are expected to treat their families with love and respect, they are expected to have only consensual sex with their wives, and they know that they will likely be faced with divorce for getting a little action on the side.
In my opinion, this change in traditional marriage is a positive one overall.
One consequence, however, is that a good man with a high libido who chooses his spouse unwisely can be put in a position of having to tolerate a life of little or no sex (after the honeymoon is over) in order not to lose his family. (The same is true for high-libido women as well of course.)
And since the wife's income plus the advent of modern, effective contraception strongly decrease the potential negative impact of spending one's resources on someone else's offspring, a high sex drive has become a very attractive and desirable quality in a wife.
Of course the correlation isn't 100%, but it stands to reason that a girl who has been interested in having lots of sex before marriage is just that much more likely to keep wanting to have lots of sex after.
Mormonism confuses the issue because it trains people not to have any sex at all before marriage -- regardless of their natural inclinations. As a consequence, among faithful Mormons, it is nearly impossible for the couple to determine whether they are sexually compatible until after they've signed on for life.
Now I'd like to ask a couple of questions of my readers, and of my LDS readers in particular, if I have any. (I probably don't have any, although it would be cool if it turns out that I do :D.) I don't intend to debate, denounce, or ridicule anyone's responses on the following -- it is a serious inquiry, and I am genuinely curious as to your position on the following:
1. Do you think sexual compatibility is an important priority in a marriage?
2. Do you think it is possible for two people to determine in advance whether or not they are sexually compatible without having sex?
3. If so, how?