Why dive bombers cannot reliably choose a battleship's weak end

From a Second World War dive bomber, is a battleship's bow or stern easier to attack than its protected midships?

Not reliably. Target motion during the dive makes precise bow or stern aiming difficult, so pilots aim to hit the ship rather than a specific weak section.

A battleship's bow or stern may be less protected than the central citadel, but a dive-bomber pilot cannot reliably select either end. The pilot may begin the attack aiming at the forward part of a turning ship. During the vertical descent the target continues moving, shifting the likely impact point back toward midships. The practical objective is therefore to hit the ship at all rather than sacrifice the hit while trying to choose a small weak section.