A lot of modern software has to ship a browser version and this simple fact can be all it takes to inform downstream choices. Let's go with WebSockets as an ex

A lot of modern software has to ship a browser version and this simple fact can be all it takes to inform downstream choices. Let's go with WebSockets as an example. You decide you need them in the browser. This will likely mean some other component will have to support them too. By now you need a pretty good reason to reimplement it over something else. If you need a handshake you may exploit the fact that WebSockets open with a standard HTTP request. Your handshake over another socket may look pretty different. DDoS services, proxies etc may support WebSockets but not arbitrary TCP or they may support it differently. A WebSocket "message" doesn't exist in plain TCP, will you make your TCP protocol work the same or will you handle frames differently? Point is - your choice may be between just WebSockets or WebSockets AND something else.