Research on the use of participatory budgeting (PB) in urban politics has, perhaps not surprisingly, found that PB participants are often coopted by the government. From a realist perspective, however, it is more surprising that cooptation does not always occur and the mechanisms of non-cooptation are still not well understood. Previous research has often explained successful outcomes in terms of the ideology of incumbents or the strength of social movements demanding participation. In contrast to both these explanations, this article suggests that an important part is played by the political interest of political elite actors in the independence of PB participants from the government. Presenting the case of PB in Rosario, Argentina, the article finds that three conditions made it rational for political actors not to coopt participants. First, a legitimacy crisis created incentives to invest in a new field of state–civil society interaction. Second, state actors involved in the creation of the field came to invest in the meanings and values of the field. Third, the field of PB could produce legitimacy for the government by being perceived as independent. The article reasons that we can expect these mechanisms of non-cooptation to be at work in much the same way in other places under similar circumstances.