Contributor-driven content is why Forbes.com, Inc.com, etc are unreadable. It's all puff pieces for some startup, unoriginal life-hacking advice and entreporn.
“The publication is packed full of advertisements, some of which are clearly labeled as such.”
Just look at Sitepoint, Digitalpoint, virtually every web development and marketing subreddit, Warrior Forum, etc.
That's what killed Medium. Everyone started promoting it as a get rich quick scheme/easy way to market your work, so the spammers, marketers and morons came in.
The only way to avoid this issue is to heavily moderate the platform with a zero fluff/spam tolerance rule, and to boot out anyone trying to game the system.
It's pretty much why I stopped posting my work to said publications, since I realised their quality was falling so much that sites like Hacker News and Reddit had banned the publication's domain.
That said, there are decent writers there. You just have to really know where to look, since the front page/newsletters/archives are a bloody smorgsaboard of reprinted mass media articles and pointless puff pieces from social media influencers.
I definitely saw some interesting pieces of UX design and usability there, and obviously the latest Silicon Valley controversy will probably first come to light there too. So meaningful stuff exists, it's just heavily buried under tides of crap.