It manages to produce its own shows because it knows that this is the way that they can do so that people will subscribe and actually watch their shows. When you think about it, Netflix has to pay a lot of money just to get the license from well-known shows. There is always a possibility that someone will outbid them and they will not get the rights to offer the show to its subscribers.
By producing its own shows, it will make people want to watch something that only they can offer. This proved to be successful because House of Cards was widely talked about. Netflix has produced a lot of other shows since then. Stranger Things is a cult favorite for sure. Netflix pays a lot of money for its shows.