Neither of those use cases are exclusive to jupyter. You can run scripts on remote machines quite easily, and matplotlib will happily pop up a window for your charts.
The real reason is because it’s a much better workflow for data exploration and manipulation because you don’t always know exactly what code to write before you do it. So having the data in memory is really useful.
X forwarding through a terminal session to view that matplotlib plot is a bit more work than most want to deal with. Sure, you can use ranger, and set up the image viewing with uzerbeurg? or something? and set up kitty with icat, but that doesn't work with your tmux, so you have to have a separate ssh window that's not tmux'd, which is annoying and clunky, just for viewing images.
You also have to save them, and then switch to view them, which is incredibly clunky.
Or you just use jupyterlab and the problem is fixed.
The real reason is because it’s a much better workflow for data exploration and manipulation because you don’t always know exactly what code to write before you do it. So having the data in memory is really useful.