How does a user interface? For a web site, primarily with a mouse. So, single touch input. For green screen they have an array of dedicated individual simultaneous input devices (known as "keys"). In addition, green screen often provides near-immediate response, whereas touchscreens can suffer from lag either in the physical interface or the unfortunate multiprocess operating system. Finally, green screen was designed to step quickly through the interface, where web requires lots of hunting around for what you want to do.
You simply can't interface better with an application than a single process dedicated application using fixed multiple inputs with immediate response. It's like web pages are a cart and horse and green screen is a race car.