They were on patrol looking for enemy destroyers.
Clearly, the Japanese were better at looking.
In early battles this gave them a decided edge. Beginning with the sea battles off Guadalcanal our Navy had radar but the commanders did not understand what it could provide so we continued to get pounded at sea.
Once we refined (PPI) radar and trained our sailors we took away the edge that the Japs had enjoyed and began to dish it out at range long before even the best lookout could see us.