When a miner finds a block, they can put transactions in it and submit it to the other miners, in order to acquire the transaction fees and the block reward for themselves.
These transactions are signed, miners can't impersonate participants. They are also incentivized to include actual transactions instead of their own thanks to the miner fee. If they try to censor a transaction, the next miner to find a block could include the transaction in the chain anyway, so they have little incentive to withhold transactions for non-economical reasons.
They can't rewrite the history, they can only push one block on top of it.
If I understand you correctly, the "centralization" you're talking about is the whole point of a consensus protocol: to get 'decentralized' participants to agree on a single 'centralized' state.
Doesn't matter if it's PoW, PoS, PoWhatever - fundamentally, crypto is about ensuring that there is a certain group of participants (miners) that can alter the shared state, while everyone who does not belong to this group cannot.
Furthermore, the group must become ever more entrenched over time because security relies on the fact that getting into this group is hard - so supposedly, those who are in the group have no interest in acting harmfully to the network. (Which is a big assumption by itself, btw)
I find it a bit weird that blockchain tech has pretty much captured the term "decentralisation" for itself, as it has some fundamental drive to centralisation built into its core.
Yes, it's decentralised in the sense that in theory everyone can become a miner. Except this is not true: If everyone could become a miner, so could adversaries and the append-only property would be gone.
This and the specific assumptions how a monetary system and an economy should work, which are also deeply baked into the tech.