Tiered evaluation of social organizations is a typical institutional form to boost public trust in them. However, in practice, there is often a bit of a challenge where the government is quite eager to participate, but social organizations can sometimes feel a bit apathetic. This study employs rational choice theory and takes Shanghai’s P District as a case study to conduct an in-depth qualitative analysis of the motivational mechanisms driving social organizations’ engagement in the evaluation system. The study reveals that the decision-making process of social organizations regarding evaluation participation is based on rational cost-benefit-risk calculations. At the micro level, uncertain expected returns, high participation costs, and a lack of efficacy perception inhibit willingness to participate; at the macro level, the “single-center” evaluation structure suppresses organizational autonomy, while deficiencies in technical rationality and legal foundations raise participation barriers. Together, these factors result in low evaluation coverage and widespread formalism. Therefore, it is essential to transform the evaluation system from “administrative control” to “development governance”, optimizing institutional structures at the macro level, innovating technical mechanisms at the meso level, and implementing targeted empowerment at the micro level. This study elucidates the complex mechanisms underlying insufficient motivation for evaluation participation, providing theoretical and practical insights for fostering endogenous development momentum within social organizations.