I mean, - ChatGPT's UI is closed-source, so I implemented a UI that looks almost identical to ChatGPT, - While ChatGPT's AI model is closed source, it can be accessed through the OpenAI API.
Not to mention, there are already OpenAI API clones which handle running against any of the open-source models. When they get more powerful and act as an actual competitor, it'll be very nice to have open-source components throughout the stack.