Because that's where the cameras are. This way all the people offended by this "grieving mother's" act will now see that she is speaking for a small minority. Don't have any signs about here, which could/will be misinterpreted. Just show the flag and praise those defending our freedom.
The media will just report it as a small pro war counterprotest, in passing with none of the signs shown. The way they always do. Better to go up there and make Miss Cindy and her handlers "inform" all of us on PNAC, BFEE, LIHOP/MIHOP, etc, etc, etc and get the whole charade over with.