This is because the price of STEEM flucates and they payouts are correlated to the price of STEEM, and it takes more "steem" to keep the payouts growing instead of decreasing.. Also your voting power is only at 100% for 10 upvotes a day you can check your % on busy.org or steemstats.com and according to https://busy.org/@iamkunaning your voting power is only 24% right now and takes 24 hours of not voting to get back to 100%