Why does stake subtract $3.10 from my withdraw total when the Bitcoin fees was only .83 cents

Here is the answer of your question
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.