Over the past few decades, the percentage of unmarried senior couples who are cohabitating has risen significantly. In fact, between 2000 and 2006 there was a 50 percent increase in the number of Americans aged 50 and older living in such arrangements, with the figure skyrocketing to about 1.8 million, according to recent census data. Why are seniors opting to forgo marriage? Even though love may be strong, there's a variety of reasons, from personal to financial, why many seniors are taking a pass on marriage. Here are some of the most common.