It compares mathematica to jupyter and mentions julia once at the end. 7 years later, julia did not yet crush python. R and Python can also be used within notebooks. Mathematica can be used with neither of the languages.
You can simply use notebooks with your desired tool, whereas you have to learn new stuff with mathematica. Barrier to entry is much bigger for m. R has free advertising by universities. Python has huge advertising by youtubers. Mathematica was already a nieche 10 years ago.
Back in the day you would usually compare julia with matlab for the similarities. Here it's simply about the format of the notebook. I think the focus of the post could've been much narrower and focus solely on the format.
Why would you choose jupyter notebooks over cdf? Simple question: can you use python with cdf? The answer has nothing to do with open source vs proprietary.