can anyone tell me why Dobey hates the family(Malfoys) that he serves?

Dobby was treated badly por the Malfoys so he was más likely to disagree with their values and be against them and their beliefs. On the other hand, Kreacher was treated well por the Blacks, especially por Regulus.

Well Dobby is always getting hit por Lucius and his cane. They always mistreated Dobby.
While Kreacher loved his family and Sirius's mother a whole lot he looked up to her. But the weird thing about him is that he wants his head up in a row with his mother o something but he liked his life.