Probably their feast or famine stage. I think it's like psuhoffman and Terpeast said, the changing climate is probably shifting the Hadley cells and speeding up the NS with not as much digging south. That means more Miller Bs which favor 40N and less opportunity for us. But if that trend continues, then we'll probably see a lot more New England exclusive Miller Bs in the future.
Even Philly got 45% more snow than BWI since 2010, which is also ridiculous. From the late 19th century to 2010, they averaged 3% more snow than BWI, and actually had many decades with less. Some of their recent disparity was certainly luck, especially 2013-14.