His father isn't stupid. He's just one of those guys who are do stuck in his ways that change makes him uncomfortable. Also, he's seen what money can do to people.
After seeing the memory of his mom, and the image of the "backer" over Shaokang, I have a hopefully untrue suspicion that his mom is either the backer or related to the backers.
Honestly his mother being a cultivator undermines everything MC has been through. At first he was just nobody who reached the top, now he is son of almost strongest cultivator on earth. Also it is poor excuse to include stronger oponents.
Yeah good job mom you sure protected your son and husband while they both died in the gutter, im sure you must be proud of yourself for your sacrifice.