Externally supported Public Financial Management (PFM) reforms often have limited success in developing countries. The reforms commonly introduce new laws and systems that are not fully implemented or used, especially by distributed agents—budgeters, accountants, and such in sector ministries, provinces, and districts. This article asks why this should be expected and what could be done about it. It builds a theory of institutional change and tests such using data from a survey of public sector accountants in Eastern and Southern African countries—one sub-set of which was distributed. The evidence supports a simple explanation of why distributed end users often limit PFM reform success: they are likely to support incumbent institutions and question reform alternatives and are less engaged in reforms than more concentrated agents who champion reforms. The article suggests that research and practice needs to better account for the influence of distributed agents on externally supported reform success.