It was probably because Nicholas II's goal was not just "to enter Blood Butterfly Valley."
But to go to Blood Butterfly Valley "with enough test subjects."
Destroying this nameless village was merely to gather materials.
If he were to attack human settlements outside—unless it was underground, it would almost be impossible to gather so many "materials." He would definitely be discovered by people before he could start his experiments.
This nameless village was on the edge of civilization.
Even if the entire village was destroyed, it wouldn't be discovered for two or three days; and even if it was discovered, it wasn't certain the discoverers would report it.
Annan had already checked the whole village.
Nicholas hadn't taken any valuables—they were all piled up in the middle of the village, in a blank square. Thus, they weren't burned.
Anyone entering the village could see this pile of valuables.