We charge the average transaction fee
https://ycharts.com/indicators/bitcoin_average_transaction_feeWhat we spend on fees on average is actually significantly more than that on average because of the number of inputs in play.
Your transaction happened to use very few inputs and was during a non-peak time. Before you made your transaction we do tell you what the fee is and you do have the option to use coins with lower fee. But we would like to offer economy fee options going forward.
They don't pay less withdrawal fee for every withdrawal. Stake charge a fixed withdrawal fee, but our withdrawal tx fee depends on the condition of Bitcoin network and the number of inputs in our withdrawal. Probably your withdrawal went through the same condition like that users. As a result your withdrawal was sent with the lower fee.
The big difference between the costs in a few of those is mainly because of the market. However, the reality is that stake is charging (and not even charging, then are using that) less than some of the exchanges and that is a big deal.
Think about it, exchanges have absolutely no risk, they are not risking anything when they let you trade, it is person A versus person B trading between each other and the exchange makes money based on each trade, and they are still charging more than Stake. Whereas Stake ends up basically just focusing on not losing money, because you could come here and take their money away from them, and yet they are still offering less withdrawal fee.