This study investigates the motivations behind cross-sector collaboration between the nonprofit and business sectors to provide social good jointly. We chose the empirical setting of Chinese charitable trusts, which emerged as a novel nonprofit avenue following the enactment of China's first Charity Law in 2016. The law designated charities and for-profit trust companies as eligible trustees, creating the potential for collaboration. Drawing resource dependency, transaction cost, and institutional theories, we employed a mixed-method design to analyze both quantitative data from 1,227 charitable trust filing documents and qualitative data from 31 semi-structured interviews conducted with key stakeholders of charitable trust likelihood of forming formal collaborations increases with growing trust asset size, term, and a positive temporal trend. The thematic analysis of the qualitative data provides richer explanations for the motivations behind cross-sector collaboration between nonprofits and for-profit trust companies. While the findings deepen our understanding of the regression results, new themes emerged, such as cases of cost-ineffective collaboration due to innovation and policy advocacy considerations within the evolving institutional environment. These findings contribute to the literature on cross-sector collaboration, offering insights into the specific factors that drive joint private provision of public goods in a non-Western context.