Why is it that there are few interracial marriages?

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I am a college student and today my professor told us that the interracial marriage rate is something like 2%. Keep in mind that fewer people are marrying these days and are simply co-habiting. However, the marriage rate for intterracial couples is still very very low.

Interracial dating is quite common.

Can someone clue me in? Please share with me your personal experiences whether you are in an interracial marriage or why you would not want to be in one.
That statistic is recent and is for the entire U.S. population. My professor did mention that this may not appear to be the case in places like southern California or other large metropolitan areas that are more diverse.
There is a difference between interracial marriage and interracial dating. It is fairly common for people to date outside their race, especially in their youth. What I couldn't understand is, why is it more common for people to DATE outside their race but not MARRY.