Forking requires consensus among the decentralized miners. If the majority of the minors didn't agree to fork, they wouldn't have been able to fork the chain.
One entity decided they were sad about code being law and decided to roll back the outcome of a faithfully executed smart contract using their influence. When one person can influence enough miners to make it the principle chain simply to undo what is in their opinion an outcome they disliked, that's centralization. Or at least a plutocracy.
Today that power rests principally with Jeremy Allaire since of course only one chain can represent the real world dollars in his bank account (USDC).
The rules of a blockchain protocol are not immutable, they can and often do change. Users decide to follow the new rules, or they decide not to. The 2016 fork showed that the majority of users and the market chose to follow ETH instead of ETC. In a few days we will probably see another fork, and most likely the majority of users will follow the PoS chain instead of the PoW chain.
It is free to run a node, and the market can freely decide to not support a chain. This is how you end up with ETC being relatively worthless even though there was a group of "rich plutocratic elites" that tried to make it succeed.
There are "influencers" like Vitalik, EF, several client teams, and thousands of hobbyists who work on research and development for the protocol, and these people do lead the direction of the technology moreso than the average user. But this is how all open source works: a small number of people make decisions, and a much larger group of people opt-in to those choices, becoming users. This is also how you end up with multiple blockchains: not everybody was happy using Bitcoin, so some people started to develop Ethereum instead.