Cash has centralized distribution, but it's very decentralized in use. That's what makes it useful. However, sometimes people might
choose to use a centralized service provider (like a bank, or a credit card company) because it's useful. They still have the
option of using cash. What's important isn't that every single transaction happens in a fully-decentralized way: it's that decentralized transactions remain
an option. That means that banks and credit card companies have to
compete with cash, and that they can never have full control of your financial life.
The same is true of cryptocurrency. It's not a problem that centralized service providers exist. If they stop providing useful services, people can just take their cryptocurrency and go home.