He is forced to choose between blood (his son) and justice (his daughter-in-law). His "relationship" with the Bahu becomes one of a protector, often resulting in him "divorcing" his son to keep the daughter-in-law as his rightful heir. Why these stories resonate:

They may live in the same house but only speak about domestic chores or their children.

In many "progressive" dramas, the Sasurji becomes the girl’s biggest advocate, often supporting her career or education when her own husband or mother-in-law opposes it.