Statistically, they lean heavily left, and what makes more sense as an explanation for that is that it is because most major outlets’ editorial workforces are themselves unionized.

Editors, drawn from the same milieu, share these priors.

And yes, people with degrees lean left too, because academia leans heavily toward the Democrats. Academia is part of the public-sector ecosystem. Universities are funded by the government, staffed by people whose careers depend on public funding, and bureaucratic growth. Their personal financial interests line up with left-wing politics.

Once one party is fused to the institutions that hand out degrees and public paychecks, of course it will show up as "more educated voters".