-The last but maybe the most important reasons is scalability. With PoS the coin can achieve 500-1000X more transaction per second comparing to Bitcoin for example (which currently stands at about 3-4 tps.
Transaction throughput scalability has nothing to do with whether a cryptocurrency applies PoW, PoS or any other proof of resource.
Anyone claiming such a thing is either lying through their teeth or has no idea what they are talking about.