I was listening the Epicenter podcast (which I suggest to listen to), Anthony Lusardi of the ETC foundation was talking about this.
Essentially, PoW is a tried and tested concensus mechanism. You just have to look at the security of Bitcoin to know whether it works or not. Are there problems in PoW? Yes. It's inefficient and wasteful in terms of energy consumption and does not align itself with greener and more environmentally friendly drives (this is actually important and for some, crypto in general is just a no-go area simply because of the mining farms). It is however the longest running consensus mechanism and it is supposed to allow natural competition - you can join the network and get mining rewards. Obviously, it comes with its own problems of centralization, mining mostly occurs in China. Why? Because electricity is cheap and they make the miners.
To go back to PoS and to the point made in the podcast (i'm pretty sure it was in the one about ETC). Imagine a scenario where you had a majority stake in the network. Obviously that would also lead to proplems of centralization because of the higher proportion of coins you actually own for a given network. They will be worth a certain amount to the staker so they wouldn't want to give them up. The problem is, they might be worth even more to a potential buyer who wishes to "purchase" the network by purchasing those coins from highest holding staker. It might be less wasteful that PoW but it doesn't solve any problems of potential corruption.