Not sure about initially, but the big benefit to Delaware today is essentially network effects: so many companies are and have been incorporated in Delaware that there is a mountain of case law and precedent, so corporate legal teams can have a very good idea of how rulings will go if the company is taken to court under Delaware law. The state's judicial system is also set up very well at this point to handle the cases put in front of it.

(It also doesn't hurt that most businesses also find Delaware's business law to be reasonably fair and advantageous. Musk notwithstanding, of course.)