I love his family, the dad is a total jerk but he is funny and the mom is just... mom, they clearly love their son, and i see why Usaki has such an effect on him having such a father sure lowered his resistance against that type of people.
It doesn't matter that he is a 6 feet muscular guy if he wasn't in her care he wasn't eating well.
Bet that the dad was some cocky amateur starting judo and the mom put him in his place then he fell in love with her, not surprising she is one hell of a woman.