I don't have a great view of how the organization behind Jupyter operates, but I'd be really surprised if they went with Medium as a way to support themselves. What feels off is an open source project (likely by accident or unwittingly) steering users towards giving to a for-profit company.
They are very well funded by numfocus: https://numfocus.org/, at least if going by the names of orgs that are sponsors. I don't think they require any financial benefit from posting things on medium.
It is rather the attitude or non-ideology of the Jupyter contributors/team, that causes things like posting on medium or telling people to post their questions in their discourse forum. It is also reflected in the licensing they chose for their ecosystem. Though usually they are friendly and helpful towards newcomers, it has to be said.
