There is a vast diversity of factors in California that makes this state a leader economically. We have the population and we have a climate that is attractive. We have the breadbasket of the world here with our agriculture. We have tourism galore and Hollywood entertainment. The computer industry are tied in with our Silicon Valley and really has/had a foothold here. And that's only the beginning.
There is so much here already. But then there are factors that drive business away. We have heavy taxation, high property values, heavy regulation, and an unstable and unreliable power situation that has driven business away. The dot-coms became busts when people realized most were never going to make a buck.
California's generous benefits, welfare etc. has brought in many who suck up resources without contributing anything back. The politicians are wildly fiscally irresponsible and the voters just keep voting them in as well voting for expensive bond measures without thinking long-term on how the heck we're going to pay them off. Education is poor, roads are not well-maintained, radical environmentalisism cripples progress...
That's just off the top of my head.