i think engagement and a little bit of more diversified posts. For instance if let's say you are a new user and get to the trending page most likely you gonna see posts regarding hive rewards/technical hive stuff etc etc which not even members here care to see that often :P
I think the most crucial is engagement though. i don't know if we need to create something to measure and reward in a way those who engage but as an author i like to see comments and for sure it gives me motivation to write more. Or maybe more curation trails that are tied with engagement at the same time i don't know
To give you an example. Some of my posts are funny some are scientific and a lot are movies/series/anime reviews. It all depends on luck though of whos gonna see it. the same posts could earn let's say 20-40$ and have more than 10 comment or 0,30$ without a single one :P It's not just the content though it's the ways of visibility as well