Doing so would allow for the additional resources to be brought to bear and the shifting of resources around, especially funding. This is exactly why the President declared an emergency along the Southern border with Mexico, in order for him to move appropriated funds around to build his southern wall.
The other reason to declare is something I've always stressed to executive leaders. It sends a message to the public that you are taking the current situation seriously. Thus my statement above, that you can only declare too late, never too early.
After writing the above, this Politico article popped up and reflects what I have written above Trump fears emergency declaration would contradict coronavirus message
Claire Rubin shared the link above.
