Network effects and also, any chain that starts as a Proof-of-Stake chain suffers from the problem of early investors and early developers essentially controlling huge chunks of the supply (sometimes 80%+), so there is much larger centralization risk and a less distributed community. I think beginning as Proof-of-Work and then many years later transitioning to Proof-of-Stake is one of the fairest distribution methods. In Ethereum (and Bitcoin), for example, no one person controls more than 1% of the supply. That will serve to hopefully make it more resilient to collusion and cartel mechanics.