Why it's so that at the time of cash out these fees and stuffs are deducted.Is it necessary?
In comparison to what wire transfers and PayPal fees, bitcoin and other cryptocurrency have way less fee. Another good thing about bitcoin is that the fees would be same if you send $10 or $1000(given the inputs and outputs are same). And as boyshx said the fees(mostly the trading fee) taken by exchanges is their main source of income.