After the invention of the aircraft and its subsequent use in the Very Big War, the world powers came together and came up with the Plot Device Treaty, setting and expanding on the laws of war.
Partially pushed by logic and significantly pushed by Old School War Leaders, one of the articles in the Treaty bans the use of explosive devices from aircraft, and significantly restricts self-propelled munitions in general. Effectively, this means that aircraft are forbidden from carrying bombs, rockets, missiles, and the like, and that guided missiles (Such as the V-1 flying bomb) are largely prohibited although unguided rockets can exist within limitations.
The plot reasons are I want battleships to be able to be the dominant force, while still allowing aircraft. Problem is, by the time WWII shows up, the age of the battleship is gone. I also want the "Old School" admirals to want to gut aircraft, knowing well what they're doing - Kind of like the resistance against using aircraft right after the First World War.
Militarily, the doctrine was originally using aircraft as scouts, targeting aids for over-the-horizon shots, and interceptors to deny the enemy use of their own aircraft.
As we well know, nothing ever stays as what it was originally intended. Aircraft would be pressed into a ground/surface attack role somehow. While not necessary, I'm keen on the idea that aircraft carriers don't exist and ocean-based aircraft are seaplanes of one variety or another, either as a small contingent carried by the battleship itself (Much like actual WWII battleships), or cared for by a seaplane tender.
But, with traditional surface attack weapons denied to them, how would aircraft be used in surface attack roles? Tech is, largely, Late-40s, early-50s equivalent.