Many of the countries examined had such bad policies that aid did little. Other countries were so totally dependent on primary exports that aid and policy could not reduce the risk enough. The postconflict setting adds more complicated layers to conflict prevention and risk assessment. While not definitive, there are several possible reasons for this. First, there are always conflict-specific assets to any war.
Some actors do well economically from war.
Second, there are conflict-specific organizations and institutions that also have an interest in continuing war. Third, conflict itself introduces norms of violence. While political conflict usually has no connection to violence, the norms have shifted in postconflict societies. Fourth, fear increases dramatically in postconflict environments. In a polarized society, pre-emptive violence makes sense when fear is a driving motive.