It’s true by default because Blueprints are not needed outside the editor.
It looks like you’re attempting to access the Blueprint generated class through the Blueprint itself.
Rather, you should just reference the class directly.
For Blueprint’/Game/dice/D4_Dice_BP.D4_Dice_BP’
The class reference is Class’/Game/dice/D4_Dice_BP.D4_Dice_BP_C’
static ConstructorHelpers::FObjectFinder<UClass> bpClassFinder(TEXT("Class'/Game/dice/D4_Dice_BP.D4_Dice_BP_C'"));
if (bpClassFinder.Object)
{
UClass* bpClass = bpClassFinder.Object;
}