Vulnerable populations in India substantially underuse social health insurance services, leading to avoidable health care expenditures. Underuse of social programs is often attributed to a lack of knowledge or perceived value among potential beneficiaries. However, we find that program implementation quality and behavioral frictions are fundamental drivers of under-enrollment and under-use in the context of a generous social health insurance program in India. These findings recast the importance of supply-side design considerations on the effectiveness of social programs.