I'm going to defend Medium a little here, because I've worked on content abuse across a number of social media platforms, and it's a hard problem. Yes, Medium has quality issues, especially if you read the content recommended on the front page. But it's not benefiting them; they'd obviously be better off if they found high quality content to promote that attracted more platform loyalty and repeat views. It just not an easy thing to do, and Medium doesn't have the size to go to war with SEO spammers the way that platforms like YouTube do.