you were raised by them, so you have a certain ingrained care for them that goes beyond normal human feelings.
as a child, you basically imprinted on them like a duck, and that kind of deep-seeded affection is difficult to remove
you can know that they are bad, and still love them. because deep inside, you still have that ingrained sense of affection for them.
it's similar to having an abusive partner. you know it's bad, but you can't leave because your caveman brain just sees comfort