I'll be honest, I know absolutely nothing about this topic. But, I would guess that engineers prioritize safety above the functionality and aesthetics of the bridge. If a bridge is unsafe the engineer might be liable for any injuries or deaths that occur due to the lack of safety measures engineered into the design. Next, I would think engineers would focus on functionality because it is very important that a real bridge is able to function properly before you focus on visual appeal. Lastly, I think the engineer would focus on aesthetics when making a real bridge because right aesthetics are probably important in boosting the engineer's career and getting him/her noticed in their field. This is just a guess though.