I am new to mining and about a month and a half ago I picked up a 1080Ti GPU and started mining with NicheHash. At that time Bitcoin was around 5800 and my daily payout was around $3.80. Now Bitcoin more than doubled and other coins followed the suit and my daily payout is still around $3.80 I am failing to understand why - any ideas?
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.