Reasons for attraction to a certain individual is different across cultures, as well as within cultures. I recently was in India, and I learned many astonishing things about their different classes and marriage within them. I was working with low-class women, who were solely interested in finding a man who could provide for them and their future children. One of my friends was even being physically abused by her husband, but she thought it was a small price to pay for having food on the table every night for herself and her daughter. She does love her husband, but their relationship is very different from most couples living in the United States. Another Indian friend of mine is very wealthy, and he chose to have an arranged marriage. For him, marriage is an adventure of learning to love your spouse over time. Here is a picture of him at his wedding! Him and his wife had only seen each other a handful of times before the wedding.
Although this is so different from what I believe marriage to be, I respect his views and understand the appeal of an arranged marriage. An article that compares arranged marriages in India with marriages of choice in America (download the PDF of the article from this link: http://onlinelibrary.wiley.com/doi/10.1002/j.1556-6678.2005.tb00595.x/abstract), found that there was zero difference in marital satisfaction between the two groups.
What I'm getting at is there are many different studies about what makes people attractive and who individuals see as "fit to marry," but there will never be enough studies that include the reasons and characteristics of every relationship in the world. Love is love, and it can't be explained. I would even go so far as to say attraction cannot be explained either.