I wonder why does cryptonator.com fee is fixed? Can anyone explain about this tnx
Given this is a web wallet, they will be paying out any transactions from a central wallet, which will be keeping actual fees to a minimum. The extra charge will be partly to compensate them for having to consolidate every input, and partly profit. If you don't want to be paying this, then you should stop using a web wallet and take control of your own coins.
Fixed fee benefits the user since you can do a pretty big transaction on a fixed rate and won't have to pay accordingly.
But at the same time it is not beneficial for people doing small transactions.
This is incorrect. The monetary value of your bitcoin transaction has absolutely no relation to how much the fee should be. The fee depends entirely on the number of inputs and outputs in your transaction. Making a big or a small transaction doesn't matter in terms of what fee you need to pay.