To me the stigma is because of the terrible quality of the content. If I see an article on Medium I assume it's from someone who doesn't know what they're talking about.

It used to be that only passionate people would write content, but now there is this pervasive idea that you must produce content to demonstrate your expertise. Producing good quality content is really hard and time consuming and people who are only motivated by sending some expertise signal to recruiters and potential employers produce troves of garbage, often on Medium. A Medium article is the writing equivalent of an empty GitHub profile with a few unmodified forks in it.