Why is the front deck of the warship a large clearing?

Because the firing of the battleship's main gun will produce a strong muzzle storm, people in front of the main gun will be blown into the water by the storm, so fragile things (such as radar or air gun positions) can't be placed in front of the battleship's main gun, so a large area will be vacated.

Because of the hull design problem, the capital of any warship is relatively narrow (so that it can get faster sailing speed), and the narrow deck in front can't hold the main gun base at all, so it has to move backwards.

Some battleships have serious waves on the front deck. If the main gun is too far ahead, the barrel will get water.

The answer downstairs is funny. Consider it a joke. There is no need to take it seriously.