In the node world I see half of projects telling you how to install it with npm and half with yarn. In Python at least pip is a standard that always works to install, even if it doesn't solve the other problems.
Unless you're in data science. Then you'll be split between conda and pip, which is worse than npm and yarn. You can always swap npm and yarn, but can't do that with conda and pip.
Those are literally equivalent though, anything you can install using yarn you can install using npm. They connect to the same registry and use the same package.json format.
Also, pip is relatively recent. Before that, it was a mix of setuptools, easy_install and various manual procedures.