Extra profit for them, they're a profit business of course they want to maximize their profit isn't? it's still acceptable with such amount they deducted, not to mention centralized exchanges and some wallet do charge additional fees too. If the amount they charge is higher than your withdrawal, then it's a legit reports since it most likely a bug.

No one is forcing you to play on Stake, you're feel free to leave and play in some sportsbooks you mentioned above that doesn't charge any additional fees.