> http.server isn't a production-ready webserver, so people use Flask [...]

Nit, but relevant nit: Flask is also not a production-grade webserver. You could say it is also missing batteries ... and those batteries are often missing batteries too. Which is why you don't deploy flask, you deploy flask on top of gunicorn on top of nginx. It's missing batteries all the way down (or at least 3 levels down).