This is true regardless of the language in use. I’m not sure why you brought it up.

Because if you know Python, you know requests already. Or flask, or configparser, or itertools, or maybe even pyqt.

Languages all have their own 'most common libraries', which add to the time it takes to learn how to be competent in that language. If a python dev tells me they know all the syntax, but have no clue what itertools or requests are, my eyebrows go up.

There's a lot of language-specific knowledge that needs to be learned before you'll be competent in it, that people don't even think about.