Ghana's National Health Insurance Scheme has not achieved full population coverage although it is a social health insurance scheme, a model increasingly gaining weight as carrying the potential to incorporate the poor and low income groups. Bearing similarity with numerous studies on non-enrolment, socio-economic factors are found to be the most influential explanatory reasons. However, additional significant non-economic variables are identified. The study adopts the decision-making theories, and secondary literature on enrolment as the theoretical perspectives against which informants' opinions are explored. Individual interviews were conducted selectively, spreading across the desired socio-economic categories. It is revealed that the ability to pay premium, employment and income level, dependency rate, risk perception, perceived health status, health-seeking behaviour, trust, quality of service, and continuous access to information are the pervasive decisive factors. Of significance are the play of politics, chieftaincy disputes, and geographical barriers. There are also challenges with indigent selection, scheme financing, service provision and coverage extension. The study documents financial barrier as representing the greatest challenge. I recommend an improved indigent targeting method and incremental assistance to empower low income groups to enrol.