While coinbase (and other exchanges) is centralised, in what way does it mean that idea of bitcoin being decentralised is lost? It's still independent from bank

While coinbase (and other exchanges) is centralised, in what way does it mean that idea of bitcoin being decentralised is lost? It's still independent from banks (and pretty much anyone, as designed). I'm not sure if anyone expected bitcoin to succeed without places like coinbase. They still don't control (and never will) emission of bitcoin and you still have an option to trade it however you like.