There is a lot of trust involved in a cryptocurrency transfer. You have to trust your technical competence to securely mount your wallet. You have to trust the wallet you're sending money to is the wallet it's supposed to go to. You have to trust the person you're sending money todo what you're paying them to. You have to trust the network to maintain the value and convertibility of the currency you're sending and receiving. Et cetera, et cetera
In practice, nobody wants to do these things. So we see centralization at exchanges. Precisely in the way people not wanting to handle cash use banks.