The Spoils of War - 8:13
Because they actively fought against Allah and His messenger. Whoever fights against Allah and His messenger, surely the punishment of Allah is severe.
Related:
The Ornaments of Gold/43:51
"Pharaoh said to his people: "O my people, does not the government of Egypt and the rivers flowing under me belong to me? Do you not see?"
The Ornaments of Gold/43:52
Or am I not superior to this man who is vile and unable to speak?
The Ornaments of Gold/43:53
Why is he not given a treasure of gold, or why do not angels come to work with him?
The Ornaments of Gold/43:54
So he misled his people and they followed him. They were a vulgar people.
The Ornaments of Gold/43:55
When they persisted in fighting Us, We took vengeance on them and drowned them all.