Counterpoint: you have made a fun and interesting thing in Python that works great in your command line/Jupyter notebook. You want to share it with your non-developer friends/anyone who might be interested, so you need some kind of interactive GUI, and the easiest one is a web page of some kind. But you don't want to learn a whole new stack because web development is really not Your Thing.
So you use something like Dash, Streamlit, or this, which allows you to do everything in Python and put up something that looks reasonably professional but does not require a great deal of time or effort. Or get serious and do it in Flask or Django.
From your other comment: But you don't need that. You can create amazing user experiences with a plain HTML, CSS and a JS file.
What do you consider the best example material for that? The reason us Python programmers (many of whom are amateurs) are so leery of Javascript et al is because most commercial websites are so hideously complicated, and most of us are just not interested in front end stuff or we would have started out with Javascript in the first place.
I've said it before, what most Python programmers want for UI is something like Visual Basic used to do - just a simple canvas with a palette of standard UI components that can be thrown together like Lego and doesn't look like a complete mess.