Reminds me of using Tkinter with Python, while learning Python. There are other GUIs available, but finding examples of working code with a newer GUI is going to be more troublesome (but not impossible). I think it's just that the documentation has been centered around Tk(inter) for so long, most people just choose it as a default. I know Python has gotten better about GUI support (probably from the popularity in machine learning/AI usage), but with Tcl being less popular, you need to do some due diligence to find up to date documentation on modern GUI usage.