In traditional Chinese culture, society was strongly patrilineal, meaning family lineage and inheritance were passed down through the father's side. This created a conceptual distinction between the “inner family” (内, nèi) and the “outer family” (外, wài).
In contrast, Western culture uses the general term “grandfather” for both, differentiating only by saying “my mom's dad” or “my dad's dad” when specificity is needed. The existence of `姥爷` as a unique, common word highlights the structural importance of lineage in Chinese social norms. While these traditional concepts are less rigid today, the language still carries this cultural DNA, and the relationship with one's `姥爷` is often just as close and cherished as with one's `爷爷`.