Fact-checking ecosystems on social media depend on the interplay between what users want checked and what contributors are willing to supply. Prior research has largely examined these forces in isolation, yet it remains unclear to what extent supply meets demand. We address this gap with an empirical analysis of a unique dataset of 1.1 million fact-checks and fact-checking requests from X's Community Notes platform between June 2024 and May 2025. We find that requests disproportionately target highly visible posts - those with more views and engagement and authored by influential accounts - whereas fact-checks are distributed more broadly across languages, sentiments, and topics. Using a quasi-experimental survival analysis, we further estimate the effect of displaying requests on subsequent note creation. Results show that requests significantly accelerate contributions from Top Writers. Altogether, our findings highlight a gap between the content that attracts requests for fact-checking and the content that ultimately receives fact-checks, while showing that user requests can steer contributors toward greater alignment. These insights carry important implications for platform governance and future research on online misinformation.