I think it's an extreme example of not-invented-here syndrome. In many ways that leads to interesting novelties, and in others it leads to not having undo/redo until the 2010s.

In fairness the problem is not easy! JupyterLab only got document-wide undo/redo in 2021 per https://jupyterlab.readthedocs.io/en/3.1.x/getting_started/c... .