I have seen "bridge" hammocks before, I understand the concept. Even if it doesn't deflect when a person gets in it, the sleeping surface would be better described as a cylinder than a plane.

As for the Golden Gate bridge, it has a lot of steel and concrete in it (and its span is actually arched). Fabric and rope do not lend themselves so easily to forming a planar surface.

Finally, I spent a couple years in the US Navy. Never saw a single hammock on any ship I was on.

I'm sure hammocks are the greatest thing since sliced bread for their proponents. Not for me, haven't found one yet that was comfortable.