Seeing the circumstances just after marriage DM's behaviour towards santu was tolerable. But after kadu's marriage wat he is doing is not right. Throughout the show it has been shown that justice and his dharm towards justice is more important to him than his dharm towards any other relationship of his. So if somehow someone or something just points out that he is being unfair to santu then he might just be fair to her. I dont really mean romance or love, but atleast her rights in the household and some faith on her too.
Santo being used to less than minimals, thnx to her poverty is accepting all that she gets, even she needs to know that she deserves to be loved and respected.
Since no in dharmpur will dare to point this out to malik. The love between hiten and khemi shud make him and santo realize that santo deserves love and respect from her husband. Also since hiten loves khemi and he will not allow any1 to disrespect her might also make DM and santu realize that santu bears all this humiliation which she doesnot deserve. Because of hiten, khemi might get the rights of being a bahu and wife which santu does not have will make santu realize that only her malik can get her love and respect from the family.
Since DM does justice and asks others to do justice, seeing them he will realize he is not doin justice to her, so he might give her his wife's position atleast in the household which ben ba is bent on not giving.
Also i wud love it if hiten just for once says- i cant bear that my wife gets ill-treated the way your wife does.
Coz only hiten can do that