the team is playing like crap ... that might be why some folks want to stay away from Nats Park.
That too, of course...but the weather-wussiness of this area is the stuff of legends. (I will, in fact, admit that if there's major rain and/or thunder/lightning I generally won't go to the ballpark myself on a weeknight - but only because I have to go to work at 06.00 in the morning and thus have limited capacity for weeknight rain delays.)