I think the reason there are less marriages today is because there's no longer a need for marriages. The main reason people got married in the past was for procreation and survival. With all the wars and plaques, we needed to make children to repopulate the village and country. Today, we're dealing with over population in a world with limited resources.
As for survival, we now have 401K and retirement plans. We don't need to make kids to take care of us when we're older. Women no longer need a man to stay alive. She has her own job and career.
So what do people get married for nowadays? For love? What happens when the love is no longer there? They get a divorce. For companionship? They have friends and Facebook
For religion? Oh yeah, people still get married because they're supposed to or else they can't reach the highest level of the Celestial Kingdom. And they they have to make as many babies as possible so the spirits in heaven can have a body.
The world has changed and evolved. The call for marriage and making babies is not as urgent as before.