It may be that they were not allowed to respond because their task is to protect the Capital and those inside.
An attack at the Navy Yard to absorb resources then a main attack on the House or Senate or both would be under defensed.
The diversion idea came up right away but never really washed. By all accounts the team in question was “Capitol Security” but they were AT THE NAVY YARD which is a mile and a half from the Capitol. No one has said what their normal patrol might be but I’m guessing their normal job would not be to patrol for the US NAVY. If something had developed close to the Capitol these guys would have been useless for quite a few minutes. And I never heard yet whether they even had their own vehicle. I suppose they did but they might have been at a fixed post. And we’d like to know whether they actually got directed to the Capitol-—or to just go get lunch.