The notebooks were THE thing of Mathematica, at least to me. 12 years ago, as I was finishing my PhD in quantum optics, I wanted to migrate to the stack used in industry - and picked Python. Also, that way I was an early adopter of Jupyter Notebook, as it captured what was need + was open.

Now Mathematica notebooks (still remember, it is .nb) do not have the novelty factor. But they were the first to set a trend, which we now take for granted.

That said, I rarely use notebooks anymore. In the coding time, it is much easier to create scripts and ask to create a visualization in HTML.