Because Dansby's proven for the last three years not to be washed up (though his play has declined from his peak). As many have said, being in shape isn't the same as being in football shape.
I'm sorry, but I believe in good habits. I think that if you're not constantly being pushed to be focused and prepared, it's not going to happen, and you get loose. All we've heard over the last three or four years is that there isn't enough practice/workout time for players IN THE LEAGUE to be prepared and sharp for the beginning of the regular season. Washington has been out of the habit of film study, reading keys, etc., for three years.