My guess would be that they have so much SEO juice, that losing some traffic to Medium for their blog doesn't matter. Their core audience is probably immersed by the time they read their content, and in addition to their strong reputation/WoM where they host their blog is a non issue. Maybe they also believe a lot of savvy people searching SEO content arent googling and picking up the same blogspam that exists when you search these types of topics.