Why it's so that at the time of cash out these fees and stuffs are deducted.Is it necessary?
Yes because obviously, you are using their services. And these companies that are doing their job so that you can cash out and use your cryptos or turn them as fiat are paying hundreds of workers and other partners just to keep their companies running and be able to give services to people like you who complain why they charge fees and all. Just try to put yourself in their shoes, would you be going all through that effort in making those things possible for users like you if you won't get anything from it? I think not. And if you would, then man, your a saint.