When ETH was created Vitalik & friends issued themselves 70% of the supply. There were very quickly miners competing to collect the mining reward & they had interests somewhat separate from those of Vitalik & friends. So whenever they wanted to make a code change they had to get miners on board or consider how miners might respond. It was still centralized enough that it wasn't a great check on power, but it was something.

The switch to proof of stake was just Vitalik & co stealing the mining reward for themselves & removing an obstacle to doing whatever they want with the code.

Having a system where people just get paid via monetary inflation for having money is naturally centralizing. There is no merit based competition that keeps people having to earn the position of collecting the block reward. And the largest holders can collectively decide that the code is whatever they want it to be. They can double the money supply tomorrow into their own wallets. And they won't allow average users to stake without handing their ETH over to a custodian.

PoS is a snake eating it's own tail. There's no grounding, it what it is because the people who have all the money say it is & they get more money because they have money.

Bitcoin rewards people who feed it energy most efficiently. It is fairly easy for the average person to run a full node (ETH calls these archival nodes) which will not allow anyone to change the monetary policy. Anyone with a computer can reject code changes in Bitcoin. No staking or mining or majority share of Bitcoin supply needed. Anyone can compete in the mining game, no massive % of the supply needed or minimum stake limit involved. You can literally mine with a $70 jade hardware wallet if you want.