Why do long engagements tend to increase divorce odds?

A few scientific studies suggest that the length of a couple’s engagement is correlated to an increased divorce risk. This is very interesting. What does the length of engagement have to do with anything? If anything, doesn’t it show that the couple is really committed the longer they stay engaged without breaking up? Or is it that it shows they are either commitmentphobic, or that they are not sure about their partner from the get go and so they keep stalling, eventually marrying but with doubts and réservations which ultimately, inexorably leads to divorce?
It’s very interesting. Other things that tend to increase the divorce odds that I find intriguing are : for one thing, the age of the wife at marriage. The younger she is, the more likely a divorce will happen. Marry a woman under 25 and plan on having a shorter marriage than if you marry the same woman when she is over 40. The same does not seem to hold for men which is even more interesting.
Fewer kids (or no kids) is a bigger divorce risk than more kids. That is, the more kids you have, the more likely your spouse is to stay put in the marriage. Of course, then you have cases like the Gosselins and you have to wonder about these statistics.
But yea, word to Jennifer Aniston: HURRY UP AND GET MARRIED! DO NOT STAY ENGAGED TOO LONG OTHERWISE THE ODDS OF THE MARRIAGE SURVIVING START TO NOT LOOK SO GREAT.