When your mining pool finds a block, each miner is paid out according to the share of work they contributed to the pool's total work. The amount of hashrate you 'own' on Nicehash is unchanging, so if other people add more hashpower to the pool over time, you will own a smaller share of the total. Historically, the network hashrate has consistently increased over time, meaning btc returns are almost guaranteed to decrease over time for any miner.
A smaller share will pay out a smaller amount of bitcoin. So over time, you should expect to see a diminishing return (measured in btc).
At the same time, the price has increased, so a smaller amount of btc is now worth more. In your case it is just a coincidence that your payout has remained steady at $3.80.
It really isn't a good idea to be using Nicehash right now. The hack hasn't been confirmed but their system's been down for a few hours now.
– AStopher – 2017-12-06T17:58:21.597As most anyone that was using them at the time now should know, is that despite the theft of many or most of the miner's existing balances that were unpaid at that time, they are TRYING to "make good" on past balances. NiceHash VOLUNTARILY is in the long process of repaying the ~50 million stolen: In late March, 2018 or April, they repaid 30% of the "Old Balances" that were due to your BTC address you were using at the time of the theft. To check your balances: https://www.nicehash.com/miner/YOUR-BITCOIN-ADDRESS and then look down, for "OLD balances", and their payback plan.
– DaaBoss – 2018-04-19T17:27:39.617