> There are literally "central banks", and if banks don't want to give somebody a bank account, there is nothing these people can do about it. That is the result of centralized control. You can not prevent somebody from having a Bitcoin address.
Banks follow laws, which is also a hard requirement for cryptocurrency businesses. Very, very few people are banned from having an account and those bans are of categories which would also prevent a cryptocurrency exchange in that country from working with them. Note also that “centralized” is only true within a governmental boundary — a bank in Zimbabwe doesn't phone someone in the U.S. to ask whether they should allow someone to open an account, which is why I described it as decentralized because it lacks a central authority.
It's true that someone can try to circumvent those measures, which is a practice dating bank centuries, but there's an important distinction between being able to make a transaction and being able to avoid punishment for doing so. Just as most censorship happens because someone is afraid of the potential consequences for speech rather than prior approval of all communications, it's both possible and a natural extension of existing practice to start demanding that people in your jurisdiction disallow any transactions linked to a particular address or to punish people for accepting a payment after it's linked to a criminal activity. You'll never get that down to zero but cryptocurrencies make it a lot easier to block than real cash payments.
This is also the problem with anonymization schemes: governments don't say “he used Monero, guess we have to give up on law enforcement” but rather “Monero does not comply with our financial laws, any business or person caught accepting it will be fined and risk jail time”. Bitcoin laundering schemes are unproven at scale from a powerful adversary but also simply using a tumbler is risky because you're publishing a durable record of using a service designed to evade legal controls — if that's ever linked back to you, you've given the police a signed confession that you knew what you were doing was illegal. Legitimate users aren't going to pay a premium to take on that risk — especially since it would open them to charges of collusion on whatever anyone else using that service was doing — and that removes legal traffic volume, making it easier for analysis and blocking.