I assume it's because he's the gramps favorite, even more than the parentThis chapter was ridiculous. I wish the author took a few panels to give some rationale to the way Youya's family treats him. Even his parents act like he's Cinderella. Is he adopted? Is he an illegitimate child or something? Couldn't he be their orphaned cousin at least? Then the family could be jealous that they were made to take care of Grandpa's favorite and they still didn't get any inheritance.