Open-source software (OSS) fosters transparency and collaboration across various domains. Scientific OSS, built on the open-source model, has been especially valuable in supporting scientific discovery and the corresponding research communities. However, ensuring the sustainability of the community by attracting newcomers and retaining existing contributors is recognized as a major challenge for the long-term success of OSS. While previous research has studied sustainability in OSS broadly, the active involvement of scientists—many of whom lack formal training in professional software engineering—and the presence of highly interdependent projects that create a multi-project ecosystem with interconnected communities may introduce unique challenges that differ from those in commonly studied OSS contexts. In this study, we explore sustainability challenges and opportunities within the scientific OSS community, aiming to understand how these aspects align with or differ from those in previously researched OSS communities. Through a survey-based replication study in the \emph{Astropy Project}—a widely-used astrophysics OSS ecosystem—we gathered insights from disengaged contributors regarding their motivations, reasons for disengagement, and suggestions for improving community sustainability. Our findings reveal key motivations driving scientific contributions to OSS, identify barriers to sustained engagement, and propose strategies to address these challenges, highlighting areas for future research.