Crypto network fees are not fixed prices set by anyone. They float, sometimes a lot, and the reason is simple supply and demand for space in each block.
Blocks have limited space
Each block on a blockchain can only hold so many transactions. When more people want to transact than there is room for, they effectively bid for the available space by attaching higher fees. Miners and validators include the higher-fee transactions first.
Demand changes through the day
Activity rises and falls. A busy market, a popular launch, or simply peak hours in major time zones can push fees up. Quiet weekends or off-peak windows often bring them down. None of this is controlled by the reward platform. It is the open network at work.
Time your cash out
Check the fee, and if it is high and you can wait, come back during a quieter window. Then withdraw.