Research on Solomon Islands and Papua New Guinea typically offers one of two explanations for the choices voters make, and the way these choices contribute to those countries' poor political governance. The first explanation focuses on culture's influence on the expectations that voters hold of politicians, contending that the Big Man style of local leadership traditionally found in both countries has shaped voter expectations in ways that cause voters to demand local or personal benefits from MPs rather than good national governance. The second explanation hinges on rational choice models of voter behaviour and does not include culture in its list of explanatory variables. In this paper I argue that neither explanation fits well with key features of these countries' politics. Drawing on quantitative and qualitative data I show that, while voters are broadly rational and can readily distinguish modern politics from traditional leadership, culture still matters. In particular, informal institutions, associated with the countries' cultural contexts, influence voter behaviour and electoral collective action, and through this political governance.