Why didn't they make OSX years ago? They did. Almost fifteen years ago. But they lacked an important bit of market penetration until their stealth takeover of Apple in December 1996. So they also lacked useful commercial software. I jumped on the bandwagon four years later, but I've already blogged the nostalgia of my little silver cube.
I found a nice article from October 2000 while confirming the important dates. Fun review of Apple and NeXT history. NeXT Computer: when cool wasn't enough