I strongly think this is because of social media (Instagram, Twitter etc.) Most of the people I’ve interacted with said that social media increased number of readers to more than five times of what it was before.
Edits and special arts help too. Take Chain Reaction for example. The art edits are too awesome even if there are several grammar and directing errors in the storyline.
Most of the top 50 stories tend to be mostly written by authors who already have/had another one of their stories in the list. MissMj is a prime example. Others include Sarah Keiser, Alex Light etc. This is because people felt positive towards their first stories, they think the other stories of the same author would be great too. We too have the similar perceptions, right?
The length of the story doesn’t matter on much occasions. Only the storyline does. If the storyline is different from usually what we read, the story gets more reads. It might work this way: long, broad cliches (Deep Attraction) and short, crisp non-cliches(Birds of Passage)
It’s not necessary to keep the usual stories in the list. Unless an extraordinary author comes up with an extraordinary storyline, that is.
Well, then. You can brainstorm further ahead. It’s night here and my darned mind won’t work 
~AS007