That was my reaction. After Pearl Harbor, I see the Justice Society members suddenly not taking their costumed identities so seriously. They wanted to enlist and fight as their true selves, the same way they would have gotten married under their real names.
Even so, every one of them smuggled their costumes along somehow and snuck out to fight the enemy as the Sandman or Dr Mid-Nite or whatever. After all, if ALL-STAR COMICS had continued to print the adventures of Sgt Al Pratt, Medic Charles McNider, Army Airman Carter Hall etc, sales would certainly dive off a cliff.