Sure, the decline in estimated payout is usually due to either fluctuating Steem prices or how other people (especially whales/dolphins) are voting. There is a daily pool of Steem/SBD available, and votes are simply there to allocate the Steem/SBD. But the thing that has the biggest influence on payout is the price of Steem. This also affects the payout amount for your votes. Another thing that affects the payout amount for your votes is your voting strength. The more you vote, the less voting power you will have, and the less your subsequent votes are going to be worth until your voting power regenerates (which is around 20% every 24 hours). But I think the decline you saw was mostly due to decline of Steem price recently, because voting less than ten times a day won't affect your voting power. Hope this helps.