I am very new to Steemit, so perhaps I am wrong...but if Steem users are increasing each day, then the number of posts is increasing faster, so unless your followers are growing as fast, each of them will have more posts to use their 'limited' votes on each day...so you should expect to see a drop as time goes on.
Although, I do believe that if you focus on high-quality content, and forget about the prizes, then you will enjoy the experience more and that will show in your posts which will result in prizes :)