jupyter specifically discourage this by hiding the button to run the whole notebook in a menu and by not assigning a shortcut to the functionality. It's better in colab though, where at least there is a button.

The thing is that people who are not professional programmers often don't realize that this is a danger, and their thing doesn't work and they don't know that it's because they're in a weird state emanating from the random execution of code blocks. So, I mean, notebooks are useful and cool, but they're definitely dangerous, especially for people who aren't software engineers, which is likely a huge fraction of their users