I don’t think google is doing that on purpose. Search engines are supposed to remove dead links once in a while. And twitter redirecting all links to the login page, so it’s effectively making duplicate results on google, which are removed. I think that’s why google doesn’t have too many Linkedin results.

I remember the fear as a web developer in making sure changes were good before going live for this very reason. "Please don't screw up the Google bot crawler and drop the search placement." I'd love to know if Google searches hitting private Reddit pages did a similar thing.

No. Private subs still showed the topic part of the body and like 4 words of the first comment I think before clicking to see you couldn’t read more. I think r/Homekit is an example of this at one point….