Posts containing links to external sites which are not owned by the parent company are downranked or outright excluded in many social media feeds. This has been a known pattern for many years.
It's not only Facebook doing it, but they are probably the biggest offender.
Is this what's behind the "link to the article in comments" that all news outlets do on FB?
You can't even put a link in a post to Instagram; student groups post links to events and say "click the link in our profile for more information" and the same is true for local news organizations.
And it's not like we are just spamming our own links, like I like to share links to news stories to my friends, family and followers.