How does BuzzFeed make decisions around promotions?

You need to befriend someone in upper management. Generally, even if you're not very skilled, you'll make out fine in terms of career growth if you have a personal relationship with someone higher than you in the latter. Go skiing with someone, graduate (have graduated) from their alma mater, and/or laugh at their jokes. Upward mobility is damn-near impossible and requires some luck, despite the recently formed career latter in each department. You're better off leaving, taking on a bigger role somewhere, and coming back.