The underlying model is incredibly simple. You have a visual model/datastore that you manipulate and the UI changes as a result. Interactions with the UI drive events which might call out to a server or do a calculation, which in turn changes the view model/datastore and that changes the UI and so on and so forth...
You probably get that, but I've down programming with wxPython, Qt, etc. I've done Django, Rails, Flask, etc. and frontend frameworks are so much more powerful and easier to use than those old models and getting them up and running takes a few minutes. When I see how much difficulty and how much anxiety this new tech is causing people it makes me wonder if the frameworks are just covering up how easy all this stuff is and how powerful it is.
It's really exciting stuff, it sucks if people are missing that.