Medium has a built-in audience so the number of people who will see a particular post and share it on Reddit, HackerNews, etc., is higher than if you just host it on Wordpress and do all the marketing yourself.
If one ever makes the mistake of giving Medium a valid email address, one's inbox will be 78% Medium article recommendations until one gets quite aggressive with the spam flags.
It's quite easy to disable the daily or weekly digests if you don't want them. Not saying I think medium is perfect, but there are better ways to approach the problem then training a spam filter.
If I've tried to turn if off once, and either it hasn't worked or it later reverted, I'm not wasting any more time on it. I can press the spam button without even leaving my mail client. I don't work for these spammers, and I don't owe them anything.
Of course, the majority of said articles the site recommends seem to be those by someone with an existing audience/fanbase, or which already got a ton of likes and shares.
As far as someone without an audience posting an article is concerned, the chances of Medium suggesting your work this way is pretty slim.