You'd need a pretty solid reason to want users to download the Python engine to run your code in their browser every time they visit an updated version of your site though. "I like writing Python better than JS" would be a sucky excuse.
If anyone does choose to do this I hope they spend significant amount of effort making their caching and code splitting optimal.
Say what you will about Jupyter notebooks and all that, but the talent pool for Python is still at a higher level. Then, this could be the worse-is-better equilibrium, but there's also a market-for-lemons situation regarding web dev these days.
My impression was that top-dollar was being payed for web-devs, with competition from some of the biggest tech giants driving the trend. Not sure that's a market for lemons, unless you are talking about the lower-end of web dev.
If anyone does choose to do this I hope they spend significant amount of effort making their caching and code splitting optimal.