As I understand it (but I can't find a corroborating source for this), the only reason that Apple didn't make that decision sooner was that Steve Jobs fell out with Intel because they wouldn't give him the good deal he was looking for.
Steve Jobs was not running Apple when they went PPC.
John Sculley did. And he says it was his biggest mistake.
When Jobs arrived back in Apple in 97', he pretty soon became dissatisfied with Motorola(and Motorola was pissed of when Jobs killed of the clones market) and PPC and started making plans on switching to Intel.
