It was falling apart.
Exactly.
He went back to the company he had created and put the best years of his youth in to. He went back to save his first love from clueless dolts who were destroying it. Who were squandering it's potential. He went back to save Apple from the Devil he had made a deal with, because he thought it would grow the company. I'm pretty sure he was the only person who could have saved Apple at that time.
Don't get me wrong. I think Steve Jobs was an azhole on many levels. He deserved to get fired the first time. But I do give him credit for going back and turning it around. It was a bold move. At the time, the smart money said it was almost a sure losing bet. Why jump on board a surely sinking ship for the final drop beneath the waves and probably get the final blame?
Sure, Next wasn't doing great, but with his name recognition he could have gotten any number of safer CEO jobs in Silicon Valley. It was a huge roll of the dice. And I think he had matured and learned a lot during his years in the wilderness. He was a much smarter CEO when he came back, and the turn around he pulled off was really quite amazing.