Why is it important to you that he left?

So that the network doesn't have a King that reigns over the decisions made on the network like Vitalik does with Ethereum

Why do you think he left..?

Tough to say. Some think he was worried the CIA would find him and either kill him or lock him up? Maybe he knew the network was in good hands at that point & could only thrive without a leader? Maybe he was interested in pursuing other interests?