It is the subjective opinion of large steem power holders as to whether your post is contributing more to the value of the project then the other thousands of posts they could potentially vote for each day. Whales, like everyone else, have a limited number of votes available to them each period.
The longer steemit is in operation, the more likely it is that voting power will become widely distributed.
Your best bet is probably to keep on posting and hope that voters think that you are contributing wothwhile content (in their subjective opinions).