The big reason that D.C. makes the cut is population density. The entire district is basically an urban area, which leads to higher insurance rates. According to Census information, D.C has a population density of 11,020 people per square mile. While this number is certainly smaller than New York City, which clocks in at 28,256 people, it puts it well above other large cities, such as Houston and even Los Angeles.
In the states with no-fault insurance, insured drivers are typically paid for medical expenses by their own insurers, regardless of who caused the accident. Nonetheless, BI liability coverage is still required in no-fault states because if injuries are bad, the at-fault driver may be sued by the injured party. If that happens, your BI coverage can help cover your liability expenses.