These pools are made up of thousands of individual miners that can direct their hash elsewhere if there is a problem. Just because pools are big does not equate to centralization. There will ALWAYS be 1-2 big pools as people will ALWAYS mine with a pool that gives them the most sats for their hash. It takes a miner 5 seconds to switch pools. If there is a censorship problem or a pool near 50% people will point somewhere else. This has happened over and over again. Bitcoin mining does not have a centralization problem just because some pools are big.