Another bridge of a starship sitting in the ship's most vulnerable spot as if you needed an officers eyeball to see things like in a sailing ship. You would think someone would learn from the Borg and protect the control center from the catfish and others. At least it retracts like a periscope.
1.) When the Ancients built the ship, there weren't many other races at the time, and none that seemed to be hostile. Their design choice wasn't born out of the need to protect that bridge to such lengths considering the ship already has good shields. The ship isn't a war ship.
2.) The entire bridge platform, if you noticed, recedes into the ship, so if things get bad, it ducks down inside flesh with the ship, the entire bridge section moves up and down, as they showed. This could give it added protection in a fire fight.
And anyway, humans didn't build this ship, it wasn't built with human thinking, it was designed by aliens, called Ancients, who think differently than us, and design differently than us.