Well I think, If you are wondering why PoS is better and necessary for the future(correct me if I am wrong): Ethereum is mined. So, by switching the PoS it decentralizes the currency further (by decentralizing hardware) because the source is not from the miners of just miners it is from the (hundred) thousands who hold it. Remember hardware is easy to detect and is vulnerable to hackers. PoS focuses on the coin which is has a higher attack resistance and can be easily hidden. TL;DR Decentralized hardware, less prone to attacks.