Another problem is, PoS coin consume much less energy, so the cheapest way to get the coin in fact is to start another PoS coin, it is much easier to clone the PoS coin, while you can't clone the bitcoin network hash power
Starting another PoS coin works just as great as starting another PoW coin trying to replace Bitcoin has worked (Litecoin and other failures, maybe only Doge has a small chance to make Bitcoin share some of its success).
Just take a look at all the NXT wannabes (pure NXT clones and those with modifications and even original PoS code cryptos), none has been able to reach the activity and market cap of NXT and that even with all the criticism on NXT's poor initial distribution - people tend to buy NXT regardless (granted all cryptos are in a bear market), because you can't easily clone core developers, infrastructure, network of nodes, vested interest, the spirit of innovation.