Maybe your followers have many other followers so not all of them see your posts. Maybe other user´s followers have more Steem Power. Voting bots also has a big impact on rewards, but their algorithms are usually secret so there is not much to do in that field.

The post timing is very important because a lot of people only vote during curation period and if you do not post when they are online, your article goes to the bottom of their feed and most people never reads it.