Jupyter came from the scientific community (originally the IPython Notebook - IPython itself was made by a physics grad student).

The use case is basically a scientific journal. You collect data. Analyze it. Make plots. Write notes (e.g. with equations, or diagrams). All in one place.

Then you can share the notebook with anyone else. If they have similar data (in the same format), they can execute the notebook on their data and get the plots all in one place.

It's great for data oriented work. It was never meant as an IDE replacement, nor as a general purpose development environment.