Board Thread:Skyrim/@comment-107.7.27.190-20130329180724/@comment-7407991-20130329184753

Because he was killed. Haven't you noticed that dragon skull above the Jarl's throne in Dragonsreach? It's Numinex's head, he was beheaded. Which is why Alduin wasn't able to raise him from the dead like the other dragons; his remains weren't intact.