>I just thought, maybe because there are hundreds or thousands of posts each day, and not everyone is being noticed...

This is a big part of it. They can't be everywhere all the time, but they have a very wide distribution and then because they support community curation, the curators of the community choose too.

>as there are a lot of factors to consider, not just the authenticity and quality of the content.

Not an easy job at all. Good luck with it.