Probably, because of the death of his mother, Rachel, Joseph became: the special object of his father's love and favor.
Joseph was the first son of Rachel and Jacob. This can be read in the bible, namely Genesis. Rachel died giving birth to her second son, Benjamin. Jacob had other sons, by his first wife Leah and servants. But he had a special love for Joseph. When he was a teenager, Joseph had dreams of grain and other indications that he would become a great ruler, and this made his brothers very jealous and they wanted him dead. There is a lot more to this story which can be read in the bible.
