There are many classic WWII stories and movies with details of fighters jumping other fighters or bombers from "coming out of the sun". So, it made it into the game.
Sunglasses in the 40's prolly not quite as good as they are today, and even today, the sun low on the horizon can keep you from seeing things (which is why I park the bike and get some coffee at sunrise/sunset rather than take the risk of that coffe-spilling, cell-phone-talking, back-seat-child-beating, putting makeup-on-it-the-mirror cager driver may not actually see me in the bright sunlight).
It's a environmental hazzard. Another obstacle to deal with and overcome.
Yeah, a royal pain at times, but I've used it to my advantage more often than it's hindered me, so I live with it.