Comment by derriz

For me, the “whole point” of TCP is to add various delivery guarantees on top of IP. It does not mandate or require a particular API. Of course, you can provide a stream API over TCP which suits many applications but it does not suit all and by forcing this abstraction over TCP you end up making message oriented applications (e.g request /response type protocols) more complex to implement than if you had simply exposed the message oriented reality of TCP via an API.