Why do they always ask if you are related to somebody who works there on job applications?

why don't employers care more about hiring the best candidate rather than the best relationship? There is enough nepotism going on in the business and political world. If everybody got what they deserved the world would be a much better place and this type of questioning only contributes to the problem. I am not interested in the legality of it, I am interested in the morality of it. Just because you can do something and avoid criminal prosecution or civil liability doesn't make it ok