Many OGD-based applications play a key role in making public data usable, yet most are short-lived because their sustainability hinges on the continued engagement and connections of independent developers. This study investigates how developer motivation and networking shape the long-term sustainability of such applications. Drawing on an exploratory case study of two mobile OGD-based applications that have been maintained for over a decade, we analyze the temporal evolution of motivational drivers and networking dynamics. Our findings show that sustainability depends not only on strong initial intrinsic motivation, but also on later obligation-based drivers, predictable maintenance demands, data-access conditions, and the changing strength of external ties. We derive six propositions that extend prior research by highlighting the temporal fragility of developer engagement and the conditional role of networking as a multiplier. Practically, the study offers insights for independent developers seeking to manage maintenance burdens and sustain long-term involvement in OGD-based initiatives.