Its not a new idea, arthur c clarke wrote about a rail launcher in Prelude to Space (1947), he based most of that story on how the scientists at that time expected space travel to happen.
No rail launchers arent new, they just havent been invested in for space travel. At a guess id say because they are expensive and end up stuck in one place, which adds limitations later on
bringing a science fiction concept into reality presents an engineering challenge that requires both research and innovation; research to find what the real life problems stopping you are, and innovation to solve them