I explained earlier.  Forget trying to analyze what PoS is (a recursive, closed loop system).  Instead figure out why Bitcoin actually is a decentralized currency.  The answer is:

The purpose of mining is to create a permanent two way peg, decentralized exchange, which thus results in a permissionless system.

Once you remove the mechanism of a permanent 2 way peg with our world and the computer world, it turns into a closed entropy system, which is the equivalent of 1's and 0's being trapped on a floppy disk and not decentralized anymore.

It's the difference between a living and evolving organism vs a video game AI script.