Cause if the story disappointed you, it was originally meant to be super dark after the 2nd island. Basically, as the Cyber-corruption progresses, he's on eternal agony, always in mind splitting pain. Every breath is meant to be a colosssal effort. He begins to lose the sense of touch, so he can no longer feel the wind when he runs. He even starts to forget his own name. Everything that matters to him, besides his friends, is stolen from him. Then, right as he achieves his goal, supposedly saving his friends, it turns out he just summoned Death itself. In the original story, he was meant to be properly dead till his friends collected the chaos emeralds to heal him, but the corruption overtakes him as he kills the End, and you get a boss battle against evil sonic. But instead we got him being dead for like 10 seconds, and the corruption being a mild inconvenice