Why the U.S. Navy built the Oregon City class

What was the purpose of the Oregon City-class heavy cruisers?

The U.S. Navy still wanted heavy cruisers after wartime losses, and the Oregon City design supplied that requirement with an updated, heavier anti-aircraft arrangement.

The institutional answer is direct: the U.S. Navy had lost ships and still wanted heavy cruisers. The Oregon City class met that continuing requirement with a revised design and a heavier anti-aircraft fit. The ships are best understood through fleet replacement and incremental improvement rather than searching for a revolutionary new role.