The short answer would be because the Delaware courts are favorable toward big business, much like New York. A long case history biased in favor of you, the bus

The short answer would be because the Delaware courts are favorable toward big business, much like New York. A long case history biased in favor of you, the business, is much more useful to you than a case history biased in favor of the consumer (California). Legal troubles of any sort are a tremendous waste of expense and time and can cripple any company, big and small. That alone is worth incorporating in a company-friendly state.