Indeed regular Jupyter works so well on VS Code for solo work these days that there is no real need for a new entrant.

So what pain point are these new entrants trying to solve?

Sure there is an issue of .ipynb basically being a gnarly json ill suited for git but it is rare that I need to track down a particular git commit. Even then that json is not that hard to read.

Also I'd like an easier way to copy cells across different Jupyter notebooks, but at the end of day it is just Python and markdown not very hard to grok.