I can enter at any time and its marginal. So I don't need to control a large share of tokens. For instance, Ethereum's proposed proof of stake requires a minimum of 32 ETH to participate or $144k at today's valuation. This is required since you need to have something at stake in case you're dishonest. And this minimum will grow as the network grows.
There's already been decisions made with this in mind. For instance, during the DAO hack, a big consideration when considering a hard fork was that the hacker got a sizable portion of all ETH. Knowing that Ethereum would move over to proof of stake in the near future, that was simply unacceptable so they decided for a hard fork invalidating the stolen funds.
Ether already suffers from concentrated ownership and has practically no defined monetary policy. So it's very centralized. Switching to proof of stake will further centralize control.
Proof of work however anyone can start / stop mining at any time with no resistance, making it more decentralized.
There's already pooling solutions for staking and more coming online such as https://rocketpool.net that do not have minimums.
Ethereum doesn't have a monetary policy, it has a security policy: the minimum issuance necessary to secure the network.
You can't simply start mining to any significant degree on Bitcoin without setting up a data center filled with customized ASIC chips that are useless for anything else but mining Bitcoin.
At least Ether's current proof of work mining is GPU based. And at least the GPUs will be valuable for AI and graphics rendering after the network migrates fully to proof of stake.
Ethereum has more than 200K validators on the proof of stake Beacon chain right now and is expected to rise dramatically as the Merge gets closer. It is highly decentralized.
There's already been decisions made with this in mind. For instance, during the DAO hack, a big consideration when considering a hard fork was that the hacker got a sizable portion of all ETH. Knowing that Ethereum would move over to proof of stake in the near future, that was simply unacceptable so they decided for a hard fork invalidating the stolen funds.
Ether already suffers from concentrated ownership and has practically no defined monetary policy. So it's very centralized. Switching to proof of stake will further centralize control.
Proof of work however anyone can start / stop mining at any time with no resistance, making it more decentralized.
[0] https://www.gemini.com/cryptopedia/the-dao-hack-makerdao