Because after Steve Jobs was fired it made him a man who would never rest on his laurels, or worse yet seek an early retirement like Bill Gates. Being sacked gave Jobs something to prove, and looking at the last decade at Apple boy did he ever prove it. And I don’t think that Jobs would have shined as bright as he did if it weren’t for the fact that he was in exile for over a decade from the company he co-founded.
Apple today also owes a great deal to the company that Steve Jobs established while he was in exile. Under the surface of every modern Mac, iPhone and iPad is the NeXTSTEP operating system that he developed back in 1985. Even the ability of Macs to run on Intel chips owes a great deal to the variety of chips that NeXTSTEP was designed to run on after NeXT exited the hardware business.