Those people aren't usually a professional business that claims to be objective and scientific in order to get customers.
You'll note that one minute melee, or that other channel that decides the fights based off voting don't get nearly as much criticism. It's just Death Battle's attitude of "we scientifically proved ourselves correct and there's no room for argument" attitude that rubs people the wrong way. Especially since a lot of their "science" is questionable at best.