Since we don't actually need visa or mastercard, but they make it damn convenient to buy stuff.
Similarly blockchain got their equivalent of this.
Right, that's why the whitepaper is titled "Bitcoin: A Peer-to-Peer Electronic Cash System". The idea is to bring many of cash payments features to the digital world, which are not possible with payment systems with intermediaries: uncensorability (nobody can keep you from transferring cash); non-reversability (no chargebacks, escrow systems are optional); low fees (contentious because BTC decided not to scale on-chain, but that was Satoshi Nakamoto's idea.