Of the more than 3500 riders who make up the numerator of this statistic, 40% get off at Anacostia and 20% at Minnesota Ave, affectionately known as the downtowns of their respective wards (8 and 7). The reason nearly 5 times as many people take the train to Farragut North as to all East of the River stations combined is obvious: Land use.
The Anacostia and Minnesota Ave station areas offer fairly similar non-residential uses, which include a limited number of destinations one would commute to on a weekday morning. Both have a few schools nearby, one relatively new District government office building, a smattering of small retail stores and restaurants, mostly carryout, and a number of light industrial sites.
Anacostia has a couple additional office or medical buildings, while Minnesota Ave boasts a grocery store. For those who do commute to work or school in these neighborhoods, parking is cheap or free, and buses often offer a superior option to rail for those who are traveling between East of the River neighborhoods.
But what about the chosen few who do take Metrorail to these 7 stations? In contrast to the system-wide statistics, 63% of trips ending east of the river originated in DC, 28% in Maryland, and 9% in Virginia. The share coming from the suburbs is certain to increase when the federal Department of Homeland Security campus at Saint Elizabeths is completed.
Interestingly, 9% of riders traveling East of the River boarded at the Columbia Heights or Georgia Avenue-Petworth stations. Without additional data, one can only hypothesize why so many people (relatively) are making this specific commute. One driver may be the schools. For example, Thurgood Marshall Academy, a high performing public charter high school across the street from the Anacostia metro station, draws students and teachers from all over the city.
Perhaps WMATA could release a subset of their data showing trips made with discounted student passes? That would make it possible to further explore this hypothesis.